abstract. One of the principal aims of the U.S. Constitution was to give the federal government authority to comply with its international legal commitments. The scope of Congress’s constitutional authority to implement treaties has recently received particular attention. In Bond v. United States, the Court avoided the constitutional questions by construing a statute to respect federalism, but these questions are unlikely to go away. This Article contributes to the ongoing debate by identifying the Offenses Clause as an additional source of Congress’s constitutional authority to implement certain treaty commitments. Past scholarship has assumed that the Article I power to “define and punish . . . Offences against the Law of Nations” is limited to customary international law. But the Framers of the Constitution understood the law of nations to include both custom and treaties, or what they called “the conventional law of nations.” The history and purpose of the Offenses Clause show that it was intended to reach treaties and—despite the prevailing view in the academy—that Congress and the Supreme Court have shared this understanding of the Clause through most of our nation’s history.

authors. Sarah H. Cleveland is the Louis Henkin Professor of Human and Constitutional Rights at Columbia Law School. William S. Dodge is The Honorable Roger J. Traynor Professor of Law at the University of California, Hastings College of the Law. We each worked on some of the cases addressed in this Article while serving as Counselor on International Law to the Legal Adviser at the U.S. Department of State, from 2009-11 and 2011-12, respectively. We also submitted an amicus brief in Bond v. United States, 134 S. Ct. 2077 (2014), based on an earlier draft of this Article. The views expressed here are our own and do not necessarily reflect the views of the State Department or of the United States. We would like to thank Vikram Amar, Ashutosh Bhagwat, William Casto, Paul Dean, Scott Dodson, Michael Dreeben, David Golove, Daniel Halberstam, Oona Hathaway, Duncan Hollis, Chimène Keitner, Andrew Kent, Geoffrey Klineberg, Harold Hongju Koh, Martin Lederman, Evan Lee, Anton Metlitsky, Henry Monaghan, Gerald Neuman, David Pozen, Zachary Price, Michael Ramsey, David Sloss, and Carlos Vázquez for their insights, comments, and suggestions.

Introduction

One of the principal aims of the U.S. Constitution was to give the federal government authority to comply with the United States’s international legal commitments.1 In recent years, Congress’s power to implement treaties has received particular attention from both the legal academy and the Supreme Court. Scholars have debated the application of federalism principles to treaties and whether the combination of the Article II treaty power and the Necessary and Proper Clause gives Congress constitutional authority to regulate matters that would otherwise lie beyond its Article I powers.2

Last Term, these debates reached the U.S. Supreme Court in Bond v. United States.3 The defendant argued that Congress lacked the power to apply the Chemical Weapons Convention Implementation Act of 19984 to her attempt to poison a romantic rival with toxic chemicals.5 In the end, the Court avoided the constitutional question, holding as a matter of statutory interpretation that the Act did not reach Bond’s conduct in the absence of “a clear indication that Congress meant to reach purely local crimes.”6 Justices Scalia and Thomas, on the other hand, would have held that the Necessary and Proper Clause does not give Congress the power to implement treaties,7 while Justices Thomas, Scalia, and Alito were prepared to impose subject-matter limitations on the treaty power.8 Justice Thomas predicted that “[g]iven the increasing frequency with which treaties have begun to test the limits of the Treaty Power,” the chance to address the constitutional limits on Congress’s authority “will come soon enough.”9

This Article contributes to the ongoing debate by identifying and comprehensively exploring the role of the Offenses Clause as an additional source of congressional authority to implement certain treaty commitments. That clause gives Congress the power “[t]o define and punish Piracies and Felonies committed on the high Seas, and Offences against the Law of Nations.”10 Past scholarship has commonly assumed that the phrase “the Law of Nations,” as used in the Offenses Clause, refers exclusively to customary international law.11 Under this reading, Congress may rely on the Offenses Clause to legislate regarding a rule of customary international law, but if Congress wishes to enact legislation to implement a treaty, it must invoke some other authority, such as its commerce power or the Article II treaty power coupled with the Necessary and Proper Clause. This Article demonstrates that this conventional academic wisdom is mistaken and that the Offenses Clause constitutes an additional and complementary source of authority for Congress to implement certain treaty commitments.

We attribute the conventional and narrow reading of the Offenses Clause to the intensive focus of foreign relations law scholars over the past thirty-five years on the Alien Tort Statute (ATS).12 The ATS uses the phrase “law of nations” to refer to the unwritten law of nations13 in contradistinction to treaties, providing district court jurisdiction over any civil action “by an alien for a tort only, committed in violation of the law of nations or a treaty of the United States.”14 Most scholars have simply assumed that the phrase “law of nations” in the Offenses Clause must have the same limited meaning that it has in the ATS.15 Yet this is a dangerous assumption. The term “international law,” for example, is generally understood today to include both customary international law and treaties,16 despite the fact that it is sometimes used to refer more narrowly to customary international law alone.17

The same was historically true of the phrase “law of nations.” The Framers of the Constitution clearly understood the law of nations to include treaties, or what they called “the conventional law of nations.” The principal purpose of the Offenses Clause—to facilitate compliance with the United States’s international commitments—also supports reading its reference to the “law of nations” to include treaties. And reading the phrase broadly is most consistent with the pre-1787 history, as well as the drafting and ratification of the Offenses Clause. In other words, the most accurate modern translation of the “law of nations” as used in the Offenses Clause into contemporary parlance is not “customary international law” but rather “international law,” which includes both customary international law and treaties.18

The Offenses Clause thus formed part of a comprehensive effort to ensure that Congress could enforce all international law, and to free the United States from having to rely on enforcement by the several States. The Framers accomplished this by creating an express enumerated power to punish in the Offenses Clause that overlaps with, and complements, Congress’s authority under the Commerce Clause19 and under the Necessary and Proper Clause coupled with the Article II treaty power.20 Indeed, the Framers considered the power to penalize individual conduct to be such an important part of the United States’s overall authority to enforce international law that the power to define and punish offenses against the law of nations in the Offenses Clause is one of just three enumerated powers in the Constitution that expressly grant Congress the power to punish.21

The understanding that the Offenses Clause allows enforcement of all international law has not been entirely lost. Despite the prevailing view in the academy, Congress, the executive branch, and the Supreme Court have shared this understanding of the Offenses Clause through most of our nation’s history. When enforcing treaties, Congress has not always specified the source of its authority. But when it has, it has often invoked the Offenses Clause, at times in conjunction with its powers under the Commerce Clause and the Article II treaty power. Indeed, in recent years, Congress has increasingly invoked the Offenses Clause as authority for legislation to enforce treaties.22 Reading the Offenses Clause to reach treaties is also consistent with past decisions of the Supreme Court, which have focused on the Clause’s core purpose of furthering the United States’s “vital national interest in complying with international law”23 and have expressly recognized that Offenses Clause legislation can include enforcement of treaties.24

Reading the Offenses Clause to extend to both treaties and customary international law is as important today as it was at the Founding. International lawmaking is increasingly dominated by international agreements, including agreements that codify and expand upon preexisting norms of customary international law. It makes little sense to think that Congress could exercise authority under the Offenses Clause to punish assaults against diplomats when their protection under international law rested exclusively on custom, but that when the United States ratified the Vienna Convention on Diplomatic Relations in 1972, Congress was deprived of the authority to implement those more detailed treaty obligations through the Offenses Clause and had to rely on other constitutional grants of legislative power.

Our argument responds to some, though not all, of the constitutional questions raised by the concurring opinions in Bond.25 Justice Scalia (joined by Justice Thomas) would have held that the Necessary and Proper Clause gives Congress the power to help the President make treaties but not to implement them.26 Justice Scalia’s argument was both textual and structural. With respect to text, he noted that the Necessary and Proper Clause gives Congress authority “[t]o make all Laws which shall be necessary and proper for carrying into Execution” powers vested in the President,27 but that Article II vests in the President only the power “to make Treaties.”28 With respect to structure, Justice Scalia argued that his reading was necessary to avoid a “vast expansion of congressional power.”29 Particularly if “the Treaty Clause comes with no implied subject-matter limitations,”30 Congress would be “only one treaty away from acquiring a general police power.”31 Others have explained why this exceedingly narrow reading of the Necessary and Proper Clause and the treaty power is mistaken.32 Our argument simply renders Justice Scalia’s reading moot with respect to the implementation of certain treaty obligations, because we identify an Article I basis for Congress’s power in addition to the Commerce Clause.33

Justice Thomas (joined by Justices Scalia and Alito), and Justice Alito writing for himself, would also have recognized subject-matter limitations on the treaty power by holding that “the Treaty Power can be used to arrange intercourse with other nations, but not to regulate purely domestic affairs.”34 The Supreme Court, however, has long held that the treaty power “extends to all proper subjects of negotiation with foreign governments.”35 As Oona Hathaway and her co-authors have shown, the drafters of the Constitution understood the need for flexibility and deliberately refrained from imposing specific subject-matter constraints on the treaty power; they also intended the political branches, not the courts, to police the appropriate subject matter for treaties.36 To the extent that subject-matter limitations on treaties exist, however, they would also apply to our reading of the Offenses Clause. Congress has no power to define and punish offenses under a treaty unless the treaty is valid in the first place.

Our argument has implications for a range of other contemporary contexts—from piracy to international counter-narcotics activity—in which Congress has adopted penal legislation to implement treaties.37 As with other enumerated powers, Congress enjoys some discretion in determining how to enforce international law by defining and punishing offenses against treaties. We identify four categories of treaties that Congress may implement under the Offenses Clause: (1) treaties that operate directly on individuals to prohibit conduct; (2) treaties that require domestic legislation punishing certain conduct, such as the Convention Against Torture and the Chemical Weapons Convention; (3) treaties that clearly proscribe certain conduct, without expressly mandating punishment for its breach, such as the Vienna Convention on Consular Relations; and (4) treaties that authorize, but do not require, punishment of certain conduct, such as the UN Convention against Illicit Traffic in Narcotic Drugs and Psychotropic Substances.

I. the original understanding of the offenses clause

Modern international law is typically divided into two categories—international agreements and customary international law.38 Modern scholars have tended to impose the same two-part division on historical sources, assuming that since “treaties” are clearly international agreements, the “law of nations” must refer to the antecedents of modern customary international law, which today “results from a general and consistent practice of states followed by them from a sense of legal obligation.”39 As Andrew Kent representatively puts it, “Today’s customary international law is the closest modern analogue of the eighteenth-century ‘law of nations.’”40 This assumption has, in turn, been superimposed on the Offenses Clause, for which scholars likewise have typically assumed that the Constitution’s reference to the “law of nations” must correspond to customary international law.41 Scholars have noted that the Constitution addresses “treaties,” “agreements,” and “compacts” elsewhere, and they have assumed that the Constitution’s treatment of codified international law is limited to those provisions. Thus, for example, Eugene Kontorovich writes: “The Treaty and Offenses Clauses separately address the two primary sources of international law. This dichotomy suggests that the Offenses Clause becomes relevant only when the United States is not party to a treaty that would authorize the relevant legislation.”42 The common assumption in the academy that the Offenses Clause is limited to customary international law has been bolstered by the fact that the founding generation sometimes did use the phrase “law of nations” when referring to unwritten international law, notably in the Alien Tort Statute, which has been the focus of most recent academic scholarship regarding the “law of nations.”43

We challenge the conventional wisdom by placing the Offenses Clause’s reference to the “law of nations” into a broader context. Drawing on the dominant international law writers familiar to the Framers, as well as the writings of the Framers themselves, we show that the eighteenth-century conception of the “law of nations” was significantly different from the modern concept of customary international law and encompassed as many as four different categories of international law, including treaties.44 The broader understanding of the “law of nations” is also consistent with the purposes of the Offenses Clause, which was a direct response to one of the significant deficiencies of the Articles of Confederation—the States’ unwillingness to discharge the Nation’s international commitments, including its commitments under treaties. The Offenses Clause grew out of a 1781 Resolution of the Continental Congress recommending that the States provide “punishment” for “offences against the law of nations,” including specifically “infractions of treaties.”45 The specific history of the Clause’s drafting and ratification also supports its application to treaties. We conclude that the most accurate modern translation of the “law of nations” as used in the Offenses Clause is not “customary international law” but rather “international law,” which today includes both customary international law and treaties.

A. The Meaning of the “Law of Nations”

At the Founding, the “law of nations” was generally used not to refer narrowly to unwritten international law, but to refer more broadly to all of international law. The two authorities that the founding generation consulted most frequently—Emmerich de Vattel’s Law of Nations and William Blackstone’s Commentaries on the Laws of England—both used “law of nations” in this comprehensive sense. Vattel divided the law of nations into four categories: (1) the necessary law of nations; (2) the voluntary law of nations; (3) the conventional law of nations; and (4) the customary law of nations.46 The “necessary law of nations” was based directly on natural law. It was immutable and binding, but only internally upon the conscience of the sovereign.47 The “voluntary law of nations” was also based on natural law, but it created external rights and duties. It was also not “voluntary” in the modern sense of the word, for nations were obligated to consent to it.48 For Vattel, the voluntary law of nations was the most important category, and most of the rules discussed in his treatise fell within this category.49 The “customary law of nations” was based on state practice, like today’s customary international law, but with the important difference that nations were free to withdraw from particular rules.50

Finally, there was the “conventional law of nations,” based on express consent and consisting of treaties. Vattel explained:

The various agreements which Nations may enter into give rise to a new division of the Law of Nations which is called conventional, or the law of treaties. As it is clear that a treaty binds only the contracting parties the conventional Law of Nations is not universal, but restricted in character.51

Elsewhere, Vattel observed that “States, like individuals, can acquire rights and contract obligations by express promises, by compacts and by treaties, from which there results a conventional Law of Nations particular to the contracting parties.”52 Another prominent eighteenth-century writer, Jean-Jacques Burlamaqui, likewise maintained that “[t]he subject of public treaties constitutes a considerable part of the law of nations.”53

William Blackstone also included treaties within his definition of the law of nations. “The law of nations,” he wrote, “must necessarily result from those principles of natural justice, in which all the learned of every nation agree: or they depend upon mutual compacts or treaties between the respective communities.”54 In short, as used by Vattel, Blackstone, and others, the concept of the “law of nations” had a meaning closer to the modern concept of “international law,” which includes both treaties and custom, than to “customary international law,” which constituted only one part of the law of nations.

Individual members of the founding generation shared this approach and repeatedly referred to the law of nations as including treaties in the years both before and after the 1787 Convention. Representing the British defendants in the famous 1784 case of Rutgers v. Waddington, Alexander Hamilton expressly invoked Vattel, explaining to the court that “[t]he positive or external law of nations [is] subdivided into the voluntary[,] the conventional[,] and the customary.”55 James Iredell similarly relied on Vattel in preparing a 1791 memorandum commenting on Attorney General Randolph’s report on the judiciary.56 “The Conventional Law of Nations,” Iredell explained, “is that part of the Law of Nations arising from Treaties; which when made according to the constitutional power of the respective Countries is undoubtedly binding on the People of both.”57 And Thomas Jefferson, giving his opinion as Secretary of State in 1793 on whether the United States could renounce its treaties with France—an opinion that relied heavily on Vattel, as well as other writers—observed: “The Law of nations, by which this question is to be determined, is composed of three branches. 1. The Moral law of our nature. 2. The Usages of nations. 3. Their special Conventions.”58

James Wilson served at the Constitutional Convention on the Committee of Detail, which produced the Offenses Clause and took an active role in the debates over its language during August and September 1787.59 In lectures on law delivered in 1790 and 1791, shortly after ratification and while Wilson was a Justice of the Supreme Court, he explained that “[n]ational treaties are laws of nations, obligatory solely by consent,”60 and, again, that “there is one part of the law of nations . . . which is founded on the principle of consent: of this part, publick compacts and customs received and observed by civilized states form the most considerable articles.”61 Instructing the grand jury in Henfield’s Case in 1793, Justice Wilson stated: “[T]here are laws of nations which are founded altogether on human consent; of this kind are national treaties.”62

Justice Samuel Chase’s 1796 opinion in Ware v. Hylton63 captured the understanding of the founding generation that treaties were part of the law of nations:

The law of nations may be considered of three kinds, to wit, general, conventional, or customary. The first is universal, or established by the general consent of mankind, and binds all nations. The second is founded on express consent, and is not universal, and only binds those nations that have assented to it. The third is founded on tacit consent; and is only obligatory on those nations, who have adopted it.64

Indeed, the Supreme Court’s use of the phrase “conventional law of nations” continued into the nineteenth century.65 Leading nineteenth-century treatise writers, including Kent, Wheaton, and Halleck, followed suit.66 So the general understanding of the “law of nations,” from at least the publication of Vattel’s The Law of Nations in 1758 until well into the nineteenth century, embraced all forms of international law, including treaties.

To be sure, members of the founding generation occasionally used “law of nations” to refer to the unwritten law of nations in contradistinction to treaties, when both terms were employed together. For example, in his widely circulated pamphlet Vices of the Political System of the Government of the United States, James Madison referred to “violations of the laws of nations and of treaties,”67 while Edmund Randolph opened the Constitutional Convention with a speech in which he complained that under the Articles of Confederation, Congress “could not cause infractions of treaties or of the law of nations, to be punished.”68Similarly, the Alien Tort Statute refers separately to both “the law of nations [and] a treaty of the United States.”69This usage seems to have been common when people referred to treaties expressly and needed a catch-all phrase to refer to the other categories of the law of nations. “Customary law of nations” would not do, because the unwritten law of nations included both the “customary” and the “voluntary” law of nations.70 So they used the general phrase “law of nations,” which would encompass both the “customary” and the “voluntary” law of nations, despite this phrase’s redundancy with respect to the “conventional” law of nations—that is, treaties.

There is nothing particularly surprising about this variation in usage. “International law” is sometimes used today in the same way to refer to customary international law in contrast to treaties, despite the fact that “international law” plainly includes both customary international law and treaties.71 Such instances from the Founding era in no way suggest that the “law of nations” as used in the Offenses Clause excluded treaties. The available evidence suggests that both Madison72 and Randolph73 intended the Clause to include treaties, and the ATS (with its express reference to treaties) is commonly thought to rest at least in part on Congress’s offenses power.74

In sum, the general understanding of the “law of nations” at the Constitution’s adoption was that it included all international law—the “voluntary,” the “customary,” and the “conventional,” which is to say treaties. The fact that the phrase was sometimes used more narrowly to refer to the unwritten law of nations, when it was expressly coupled with “treaties,” at best suggests a potential ambiguity. But the Offenses Clause does not refer separately to the law of nations and treaties. Moreover, any ambiguity is resolved by the context in which the Offenses Clause was adopted, by the history of its drafting, and by the arguments made for ratification.

B. The Historical Context of the Offenses Clause

Compliance with the law of nations—including compliance with treaties—was a matter of acute concern under the Articles of Confederation. From the moment of independence, as John Jay would later write for the Supreme Court, “the United States had, by taking a place among the nations of the earth, become amenable to the laws of nations; and it was their interest as well as their duty to provide, that those laws should be respected and obeyed.”75 Violations of the law of nations were considered a just cause for war,76 a point that Jay would note specifically in Federalist No. 3.77 The Framers genuinely feared that “violations of the law of nations & Treaties . . . must involve us in the calamities of foreign wars.”78 Finally, “[n]ational honor was at stake as well, an idea the Revolutionary generation took quite seriously.”79

On June 12, 1776, even before the Declaration of Independence was signed, the Continental Congress appointed a “committee to prepare a plan of treaties to be proposed to foreign powers.”80 That committee reported a draft, which was discussed and approved on July 18.81 On February 6, 1778, the United States entered a Treaty of Alliance82 and a Treaty of Amity and Commerce83 with France. These treaties were critical in helping the United States obtain the military support necessary to secure its independence by force of arms. Over the next decade, the United States entered treaties on the same basic model with the Netherlands,84 Sweden,85 Prussia,86 and Morocco.87 In 1783, the United States also concluded the Definitive Treaty of Peace with Great Britain, acknowledging the United States’s independence.88 The United States’s inability to secure compliance with its treaty obligations under the Articles of Confederation, however, soon became apparent. In 1786, Foreign Secretary John Jay prepared a long report for the Continental Congress detailing treaty violations by the several States.89 State violations of the Treaty of Peace with Britain—particularly Articles IV and V, dealing with debts and confiscated properties—were of particular concern because they gave Britain an excuse not to evacuate military posts on U.S. soil.90

While state treaty violations attracted the most attention before and at the Philadelphia Convention, treaty violations by individuals were also of concern. The 1778 Treaty of Amity with France contained a number of provisions proscribing individual conduct and requiring punishment for infractions, some of which were repeated in subsequent treaties with other nations. Article IX provided that the inhabitants of each party “shall abstain and forbear to fish in all places possessed, or which shall be possessed by the other party” and that ships “found fishing contrary to the tenor of this treaty . . . shall be confiscated.”91 Article XV stated that privateers of either party “shall be forbid doing any injury or damage to the other side; and if they act to the contrary they shall be punished, and shall moreover be bound to make satisfaction for all matter of damage.”92 Article XXI prohibited the subjects of France and people and inhabitants of the United States from taking commissions or letters of marque to act as privateers against the other side, providing specifically that “if any person of either nation shall take such commissions or letters of marque, he shall be punished as a pirate.”93 And Article XX guaranteed safe conduct for merchants of the other nation and their goods in case war broke out, supplementing the unwritten law of nations with respect to safe-conducts.94

There were also neutrality provisions in these treaties providing for “a firm, inviolable and universal peace” between the parties and their inhabitants.95 The Peace Treaty with Great Britain similarly provided that “[t]here shall be a firm and perpetual peace between his Britannic Majesty and the said States, and between the subjects of the one and the citizens of the other.”96 During the Neutrality Crisis in 1793, individuals were prosecuted by the federal government for violating the neutrality provisions of the treaties with Britain, the Netherlands, and Prussia if they aided the French, with whom these powers were at war.97

The Continental Congress soon expressed concern about individual violations of international law in a 1781 Resolution98 that is properly viewed as a forerunner of the Constitution’s Offenses Clause.99 The Resolution expressly identified “infractions of treaties and conventions to which the United States are a party” as “offences against the law of nations”100 and recommended that the several States “provide expeditious, exemplary and adequate punishment.”101 The Articles of Confederation had granted Congress the power of “appointing courts for the trial of piracies and felonies committed on the high seas,”102 but they otherwise contained no provision allowing Congress to define and punish offenses against the law of nations, whether unwritten or conventional. This lack of legislative authority meant that the United States was largely dependent upon the several States for adherence to its international obligations. But a committee consisting of Edmund Randolph, James Duane, and John Witherspoon reported to Congress “[t]hat the scheme of criminal justice in the several states does not sufficiently comprehend offenses against the law of nations.”103

The 1781 Resolution, which Randolph drafted,104 therefore provided as follows:

Resolved, That it be recommended to the legislatures of the several states to provide expeditious, exemplary and adequate punishment:

First. For the violation of safe conducts or passports, expressly granted under the authority of Congress to the subjects of a foreign power in time of war:

Secondly. For the commission of acts of hostility against such as are in amity, league or truce with the United States, or who are within the same, under a general implied safe conduct:

Thirdly. For the infractions of the immunities of ambassadors and other public ministers, authorised and received as such by the United States in Congress assembled . . . :

Fourthly. For infractions of treaties and conventions to which the United States are a party.

The preceding being only those offences against the law of nations which are most obvious, and public faith and safety requiring that punishment should be co-extensive with such crimes:

Resolved, That it be farther recommended to the several states to erect a tribunal in each State, or to vest one already existing with power to decide on offences against the law of nations, not contained in the foregoing enumeration, under convenient restrictions.

Resolved, That it be farther recommended to authorise suits to be instituted for damages by the party injured, and for compensation to the United States for damage sustained by them from an injury done to a foreign power by a citizen.105

The 1781 Resolution demonstrates that Congress was concerned about individual treaty violations and that it understood such violations to be “offences against the law of nations.”106 The Resolution identifies as included in the “law of nations” three specific violations that were of particular concern (safe-conducts, breaches of neutrality, and immunities of ambassadors and diplomats) as well as general “infractions of treaties.”107 Notably, the Resolution twice refers expressly to “infractions of treaties” as “offences against the law of nations.” First, in the sentence immediately following the reference to “infractions of treaties,” Congress describes “[t]he preceding”—that is, violations of safe-conducts, breaches of neutrality, infractions of the rights of ambassadors, and violations of treaties—as “being only those offences against the law of nations which are most obvious.”108 Second, Congress recommends that the States appoint tribunals “to decide on offences against the law of nations, not contained in the foregoing enumeration.”109 In other words, “infractions of treaties” were understood to be “offences against the law of nations” that were “contained in the foregoing enumeration.”110

Apart from the general “infractions of treaties” provision, the Resolution’s discussion of specific violations indicates that at least some of these also covered rights established by treaty. The Resolution urges punishment for violations of safe-conducts “expressly granted under the authority of Congress,” and for breaches of neutrality against states “in amity, league or truce with the United States.”111 The United States routinely granted express safe-conducts and entered states of amity with other countries by treaty. Indeed, by the time of the 1781 Resolution, the Treaty of Amity with France expressly guaranteed safe conduct for merchants in case of war112 and pledged peace between the two countries and their inhabitants,113 thereby adding a layer of treaty protection to the unwritten law of nations. The Resolution made no attempt to distinguish violations of safe-conducts and breaches of neutrality under treaties from the unwritten law of nations.

The 1781 Resolution’s reference to treaties is also significant because that resolution—which calls for “punishment” of “offences against the law of nations”—is properly viewed as an antecedent of the Constitution’s Offenses Clause itself.114 The Clause was intended to address the same failure of the States to punish violations of international law identified in the Resolution, and the Resolution’s author, Edmund Randolph, would play a key role in drafting the Offenses Clause.115 The fact that this forerunner to the Offenses Clause expressly identified treaty violations as offenses against the law of nations, and drew no distinction between treaty violations and violations of unwritten law, strongly suggests that the Offenses Clause reaches such violations.

Only Connecticut and South Carolina passed statutes responding to the 1781 Resolution.116 Connecticut’s 1782 statute punished violations of safe-conducts, breaches of neutrality, and infractions of the immunities of ambassadors—thus addressing violations of existing treaties to the extent such treaties granted safe-conducts or promised peace117—but it did not implement the 1781 Resolution’s recommendation to punish infractions of treaties more generally.118 South Carolina’s 1785 law was limited to protecting the rights of ambassadors.119 The latter may have been motivated by the famous Marbois Incident during the summer of 1784, in which a French Consul-General was assaulted on the streets of Philadelphia.120 Because Pennsylvania had no applicable statute, Marbois’s assailant was prosecuted at common law and convicted in Pennsylvania state court for “an infraction of the law of Nations.”121 Faced with inaction on the part of the states, the Continental Congress in 1785 directed John Jay, the U.S. Secretary for Foreign Affairs, to draft “an act to be recommended to the legislatures of the respective states, for punishing the infractions of the laws of nations, and more especially for securing the privileges and immunities of public Ministers from foreign powers,”122 although there is no record of Jay’s ever drafting such an act.123 The dismal record of the states in punishing violations of the law of nations in general—and treaties in particular—provided a powerful motivation for the Constitutional Convention to vest such power in the national government.

C. Drafting the Offenses Clause

Treaty violations and other offenses against the law of nations were very much on the minds of the delegates who gathered in Philadelphia during the summer of 1787. During the previous winter, James Madison had written Vices of the Political System of the United States, which was widely circulated.124 Among these vices, Madison listed “[v]iolations of the law of nations and of treaties.”125 The rest of Madison’s discussion shows that he viewed treaties as an integral part of the law of nations. He complained specifically that “[t]he Treaty of peace—the treaty with France—the treaty with Holland have each been violated” and added that “[t]he causes of these irregularities must necessarily produce frequent violations of the law of nations in other respects.”126 In other words, violations of the treaties with Britain, France, and Holland were troubling violations of the law of nations, but they were not the only violations of the law of nations that were cause for concern.

Virginia Governor Edmund Randolph opened the Constitutional Convention with a speech in which, according to Madison’s report, he complained that under the Articles of Confederation, Congress “could not cause infractions of treaties or of the law of nations, to be punished: that particular states might by their conduct provoke war without controul.”127 Like Madison, Randolph distinguished treaties from the law of nations in this instance, but elsewhere he understood the violation of a treaty to be an offense against the law of nations. It was Randolph, after all, who drafted the 1781 Resolution for the Continental Congress that expressly listed “infractions of treaties and conventions to which the United States are a party” as “offences against the law of nations.”128

The original plans submitted to the Convention by the Virginia delegation, by delegate Charles Pinckney, and by delegate William Paterson on behalf of New Jersey, each proposed to address violations of the law of nations not through the legislature but through the judiciary.129 As George Mason described the thinking of the Virginia delegation in a letter to Arthur Lee, “[t]he most prevalent idea” was to establish “a judiciary system with cognizance of all such matters as depend upon the law of nations.”130 The Offenses Clause first emerged in a draft outline of the Constitution:

6. To provide tribunals and punishments for mere offences against the law of nations.

7. To declare the law of piracy, felonies and captures on the high seas, and captures on land.131

The draft Constitution that the Committee of Detail reported to the Convention on August 6, 1787, gave Congress the power

[t]o declare the law and punishment of piracies and felonies committed on the high seas, and the punishment of counterfeiting the coin of the United States, and of offences against the law of nations.132

This provision came up for debate on August 17, and the discussion focused on the words “declare,” “define,” and “punish.”133 James Madison moved to strike the words “and punishment.”134 George Mason questioned whether this would suggest that Congress lacked the power to punish the offenses listed, “considering the strict rule of construction in criminal cases.”135 Randolph did not think “that expunging ‘the punishment’ would be a constructive exclusion of the power.”136 Wilson agreed, noting that “[s]trictness was not necessary in giving authority to enact penal laws; though necessary in enacting & expounding them.”137

Although Madison won his motion, Gouverneur Morris successfully proposed another to strike out “declare the law” and insert “punish,”138 effectively undoing what Madison had just accomplished. This left Congress with the right “[t]o punish piracies [etc.],” at which point Madison and Randolph moved to insert “define &” before “punish.”139 Madison explained that “felony at common law is vague.”140 He did not think that felonies should be defined by English law because “no foreign law should be a standard farther than is expressly adopted.”141 But neither should felonies be defined by state law, for then “the citizens of different States would be subject to different punishments for the same offence at sea.”142 “The proper remedy for all these difficulties was to vest the power proposed by the term ‘define’ in the Natl. legislature.”143 Oliver Ellsworth enlarged the motion to amend the Clause to read “to define and punish piracies and felonies committed on the high seas, counterfeiting the securities and coin of the U. States, and offences agst. the law of Nations,” which was agreed to without objection.144

In the Committee of Style, the clause on counterfeiting was broken into a separate provision and the Offenses Clause made to read as follows: “To define and punish piracies and felonies committed on the high seas, and punish offences against the law of nations.”145 The Clause came up for debate again on September 14. “Govr. Morris moved to strike out ‘punish’ before the words ‘offences agst. the law of nations.’ so as to let these be definable as well as punishable . . . .”146 This time, the debate over Congress’s power to define focused not on felonies, but on the law of nations. James Wilson objected to the proposal on the ground that “[t]o pretend to define the law of nations which depended on the authority of all the Civilized Nations of the World, would have a look of arrogance. [T]hat would make us ridiculous.”147 Morris responded that “[t]he word define is proper when applied to offences in this case; the law of nations being often too vague and deficient to be a rule.”148 Morris carried the day by a vote of 6-5, and the Offenses Clause took its present form.149

Wilson’s reference in this exchange to law “which depended on the authority of all the Civilized Nations of the World” clearly refers to the unwritten law of nations, but it would be a mistake to conclude on that basis that the Offenses Clause as a whole was so limited. We have seen that Wilson thought that “[n]ational treaties are laws of nations”150 and that “one part of the law of nations [consisted of] publick compacts.”151 The fact that Wilson thought it would “have a look of arrogance”152 to define one part of the law of nations in no way suggests that he believed the Clause was limited to that part. Nor does Morris’s response that the law of nations was “often too vague and deficient to be a rule”153 suggest that the clause was limited to the unwritten law of nations, for there was no necessary correspondence between treaties and clarity, or unwritten law and vagueness. The prohibition against piracy, for example, although it formed part of the unwritten law of nations, was generally acknowledged to be sufficiently clear as not to require further definition by the legislature.154 Indeed, the Articles of Confederation had given the Continental Congress authority to appoint courts to try piracies without any further power to define the term,155 and the Supreme Court similarly concluded in United States v. Smith that Congress had adequately “defined” the crime of piracy by referring to the unwritten law of nations.156 On the other hand, certain treaty provisions could benefit from further definition. For example, following Gideon Henfield’s acquittal in the most prominent neutrality prosecution on charges of violating the neutrality provisions of the treaties with Britain, the Netherlands, and Prussia by aiding the French,157 Congress passed the 1794 Neutrality Act, which specified in clear terms the kinds of acts that would be punishable.158 Even if some treaty provisions were clear and not in need of further definition before they were applied, it is important to recall that Morris said the law of nations was “often too vague and deficient to be a rule,”159 not that it was always too vague.

In sum, the drafting history does not show that the Offenses Clause used the phrase “Law of Nations” in a narrower sense than the common understanding of the era, which included treaties, or in a narrower sense than the 1781 Resolution, which expressly identified “infractions of treaties” as “offences against the law of nations.”160 While the inclusion of treaties within the scope of the Offenses Clause was not specifically discussed at the Convention, those who participated in the debates—like Randolph, Madison, and Wilson—all believed that the law of nations included treaties, and their rationales for adopting the Offenses Clause applied equally to treaties.

D. Ratification Debates

The Offenses Clause received relatively little attention during the ratification debates.161 But in Federalist No. 42, Madison explained the purpose of the Clause in terms that applied as readily to treaties as to unwritten international law. Madison noted that the Articles of Confederation “contain no provision for the case of offenses against the law of nations; and consequently leave it in the power of any indiscreet member to embroil the Confederacy with foreign nations.”162

In Federalist No. 3, John Jay defended the assignment of power over the law of nations to the federal government in more general terms. But buried in this essay again is evidence to support the understanding that this power encompassed treaties. Jay observed that “[t]he prospect of present loss or advantage may often tempt the governing party in one or two States to swerve from good faith and justice,” citing “[t]he case of the treaty of peace with Britain” as a particular example.163 He then noted that “the national government, not being affected by those local circumstances, will neither be induced to commit the wrong themselves, nor want power or inclination to prevent or punish its commission by others.”164 The word “punish” makes it likely that Jay was referring specifically to the Offenses Clause. If so, he would have understood that clause to include violations of treaties, for his specific example of the sort of “wrong” the national government would be able to “punish” was a violation of “the treaty of peace with Britain.”

As Secretary of Foreign Affairs under the Articles of Confederation, Jay had prepared the 1786 report for Congress on state treaty violations,165 and it is reasonable to think that he would have been as concerned to punish violations of treaties as violations of the unwritten law of nations. Jay summarized his point in a much-quoted passage:

So far, therefore, as either designed or accidental violations of treaties and of the laws of nations afford just causes of war, they are less to be apprehended under one general government than under several lesser ones, and in that respect the former most favors the safety of the people.166

Jay’s argument in Federalist No. 3 for assigning power of the law of nations to the federal government thus parallels Madison’s specific description of the purpose of the Offenses Clause, but Jay made it explicit that this argument also applied to violations of treaties.

Another discussion of the Offenses Clause in the newspapers supports the understanding that the Offenses Clause included violations of treaties. In November 1787, the Anti-Federalist writer Cincinnatus published an essay arguing that the Offenses Clause was so broad as to threaten freedom of the press.167 A writer calling himself Anti-Cincinnatus responded with an essay in a Massachusetts paper that clearly read the Offenses Clause to apply to treaties:

[I]t is needful, to that end only to consider, that by the law of nations, is intended, those regulations and articles of agreement by which different nations, in their treaties, one with another, mutually bind themselves to regulate their conduct, one towards the other. A violation of such articles is properly defined an offence against the law of nations: and there is and can be no other law of nations, which binds them with respect to their treatment one of another, but these articles of agreement contained in their public treaties . . . .168

Certainly, the writer was mistaken in thinking that the “law of nations” in the Offenses Clause referred only to treaties. But this essay offers further proof that the phrase could be understood—and indeed was understood—to include treaties.169

The evidence from the ratification debates is limited because of the relatively scant attention the Offenses Clause received, but what evidence exists supports reading the clause to encompass all of the law of nations, including treaties. Madison’s specific discussion of the clause is consistent with this reading; Jay referred particularly to treaty violations in discussing the federal government’s power to “punish” wrongs against other countries, and Anti-Cincinnatus expressly read the clause to apply to treaties. Moreover, to our knowledge, there is nothing in the ratification debates to support the idea that “law of nations” was used in a narrow sense to exclude treaties.

E. Constitutional Design

Our conclusion that the Offenses Clause was intended to promote U.S. compliance with international law as a whole finds further support in the constitutional design. The Framers’ concern in Philadelphia was to ensure that the United States would be able to enforce U.S. international law commitments at the national level.170 The Constitution accordingly gave the President the “Power, by and with the Advice and Consent of the Senate, to make Treaties, provided two thirds of the Senators present concur”171 and the duty to “take Care that the Laws be faithfully executed.”172 It gave Congress the powers—among numerous others implicating U.S. foreign relations—“[t]o regulate Commerce with foreign Nations,”173 “[t]o define and punish Piracies and Felonies committed on the high Seas, and Offences against the Law of Nations,”174 and “[t]o make all Laws which shall be necessary and proper for carrying into Execution the foregoing Powers, and all other Powers vested by this Constitution in the Government of the United States, or in any Department or Officer thereof.”175 The Constitution provided for a federal judiciary with jurisdiction over “all Cases . . . arising under this Constitution, the Laws of the United States, and Treaties made, or which shall be made, under their Authority,”176 as well as an array of specific instances likely to raise foreign relations concerns.177 It provided that “all Treaties made, or which shall be made, under the Authority of the United States, shall be the supreme Law of the Land; and the Judges in every State shall be bound thereby.”178 And it forbade the States from exercising a range of powers relating to foreign relations, including the power to “enter into any Treaty.”179 As Golove and Hulsebosch have correctly observed:

Considered as a whole, and understood in historical perspective, the text establishes a comprehensive regime for dealing with foreign affairs with an eye equally on centralizing all of the relevant powers in the federal government and on ensuring, as far as possible, that the federal government would uphold the nation’s international duties.180

The Offenses Clause was only one piece of the constitutional scheme ensuring that the federal government had sufficient authority to secure the United States’s compliance with its international obligations. But it was an important piece—so important that the Offenses Clause is one of the only explicit powers to impose punishment that appears in the Constitution.181

The fact that the Constitution addresses treaties elsewhere creates no implication that the Offenses Clause excludes them. Powers granted by the Constitution frequently overlap.182 The Supreme Court has repeatedly held that the express grant of one power does not limit the exercise of others, often citing the Offenses Clause as an example.183 This proposition has long been clear to students of the Constitution like Justice Story, who made the point with specific reference to the Offenses Clause in his Commentaries on the Constitution of the United States. “It is obvious,” he wrote, “that this [offenses] power has an intimate connexion and relation with the power to regulate commerce and intercourse with foreign nations, and the rights and duties of the national government in peace and war, arising out of the law of nations.”184

The purpose of the Clause—to give Congress the authority to ensure compliance with international law by punishing violations—was also clear to Justice Story:

As the United States are responsible to foreign governments for all violations of the law of nations, and as the welfare of the Union is essentially connected with the conduct of our citizens in regard to foreign nations, congress ought to possess the power to define and punish all such offences, which may interrupt our intercourse and harmony with, and our duties to them.185

This rationale so clearly implicates treaties as well as customary international law that it is hard to understand why the Clause would have excluded them.

In sum, we believe that the historical evidence shows that the Framers did not exclude treaties from the Offenses Clause. The understanding of the “law of nations” at the time of the Founding included not just the unwritten law of nations but also treaties—what Vattel and others called “the conventional law of nations.” The Offenses Clause has its origins in a 1781 Resolution of the Continental Congress that expressly listed “infractions of treaties” as “offences against the law of nations.” The drafting history of the Clause is consistent with a broad understanding, and although the specific evidence from the ratification debates is limited, there is evidence that some readers understood the Clause to reach treaties, while there appears to be none to the contrary. Having established that the original understanding of the Offenses Clause embraces both the unwritten law of nations and treaties, we turn next to consider the Clause’s interpretation by Congress and the Supreme Court.

II. congressional and judicial interpretations

The Constitution draws its meaning not only from the understanding of the Framers but also from the practical construction of the document over time.186 Congress has not invoked the Offenses Clause with great frequency, but the evidence nevertheless shows a consistent congressional understanding—from the very first Congress—that the Offenses Clause authorizes Congress to define and punish all violations of international law, including offenses under treaties. Supreme Court decisions also describe the Offenses Clause as applying to international law obligations generally. The Court’s discussion of the purpose of the clause applies equally to treaties, and in several cases the Court has applied the clause to uphold legislation implementing treaties.187

A. Congress’s Understanding of the Offenses Clause

Congress often does not specify the source of its authority,188 but legislation from the 1789 Alien Tort Statute to the 2006 Military Commissions Act shows that Congress has consistently understood its authority under the Offenses Clause to extend to the implementation of treaties. These acts of Congress and other legislative materials establish two additional points. First, treaty obligations often overlap with and incorporate customary international law, and Congress repeatedly has passed legislation to implement U.S. treaty obligations and customary international law together. The interrelationship between treaties and customary international law therefore provides an additional reason not to view the Offenses Clause as limited to only one kind of international law.189 Second, the Offenses Clause is only one of several constitutional authorities that Congress may use to implement treaties. Even when Congress has specifically invoked the Offenses Clause, it has often cited other constitutional powers as well. The Foreign Commerce Clause and the Necessary and Proper Clause, in particular, grant broad authority to implement the United States’s treaty obligations. Congress has not understood the Offenses Clause to be exclusive of those other powers, but rather as an additional and complementary source of authority.190

Congress apparently first exercised its power under the Offenses Clause in 1789 by enacting the provision of the First Judiciary Act known today as the Alien Tort Statute (ATS) or Alien Tort Claims Act (ATCA)—a provision that expressly extends to treaty violations. As originally enacted, the ATS provided that “the district courts shall have . . . cognizance, concurrent with the courts of the several States, or the circuit courts, as the case may be, of all causes where an alien sues for a tort only in violation of the law of nations or a treaty of the United States.”191 Although the ATS undoubtedly rested on other legislative powers as well,192 commentators with a range of views about the statute have concluded that the ATS falls squarely within Congress’s authority under the Offenses Clause.193 It would have been natural for Congress to rely on the Offenses Clause in passing the ATS because both the statute and the constitutional provision had their origins in the Continental Congress’s 1781 Resolution recommending that the states provide “punishment” for “offences against the law of nations.”194 The ATS grew out of the final paragraph of that resolution, recommending that the states “authorise suits to be instituted for damages by the party injured.”195 Civil liability was a natural counterpart to criminal prosecution, and the power to authorize actions for damages was understood to be within Congress’s authority under the Clause.196 Like the 1781 Resolution, the ATS extended not just to violations of the unwritten law of nations but also to violations of “a treaty of the United States.” This reveals that, like the drafters of the 1781 Resolution, the First Congress viewed the Offenses Clause as reaching both unwritten and conventional law.197

Congress exercised its authority under the Offenses Clause again the following year when it passed the Crimes Act of 1790.198 The Crimes Act addressed piracy as well as two of the substantive violations identified in the 1781 Resolution, violations of safe conducts and assaults on ambassadors, thereby punishing violations of both unwritten law and treaties. Sections 8 through 12 of the Crimes Act defined and punished piracy, assisting pirates, concealing pirates, and confederating with pirates.199 U.S. treaties with France, the Netherlands, Sweden, and Prussia provided that U.S. inhabitants taking commissions or letters of marque to act as privateers against the other party would be punished as pirates.200 The piracy provisions of the Crimes Act therefore implemented these provisions as well as the more general prohibition against piracy in the unwritten law of nations. Section 28 of the Act provided punishment for the violation of “any safe-conduct or passport duly obtained and issued under the authority of the United States.”201 U.S. treaties with France, the Netherlands, Sweden, and Prussia supplemented the unwritten law of nations on safe conduct by expressly granting a period of time for merchants of the other party to remove themselves and their goods in case of war between the parties.202 Section 28 provided punishment for violations of these treaty provisions as well as the unwritten law of nations.203

The Crimes Act did not itself fully implement the recommendations in the 1781 Resolution; it did not address neutrality, and it lacked a general prohibition against violating treaties, unlike the provision of the 1781 Resolution recommending that the states punish “infractions of treaties and conventions to which the United States are a party”204 and the ATS’s clause authorizing civil suits for torts in violation of “a treaty of the United States.”205 But Congress’s failure to enact such a provision does not mean that Congress lacked authority under the Offenses Clause to do so. The assumption in the 1790s seems to have been that at least some treaty violations could be subject to prosecution at common law, jurisdiction having been granted by the provision of the 1789 Judiciary Act giving the district courts “cognizance of all crimes and offences that shall be cognizable under the authority of the United States.”206 That was the theory in Henfield’s Case, the most prominent of the neutrality prosecutions brought by the Washington Administration in 1793, which specifically charged the defendant with several treaty violations.207 Henfield had joined the French ship Citizen Genet in Charleston, South Carolina, serving as its prize master when it captured as a prize the British ship The William.208 Justice James Wilson charged the grand jury in Philadelphia, instructing them both that “under our national constitution, treaties compose a portion of the public and supreme law of the land,” and that treaties were part of the law of nations.209 “[T]here are laws of nations which are founded altogether on human consent,” Wilson observed, and “of this kind are national treaties.”210 The grand jury returned an indictment of twelve counts against Henfield.211 Six of these counts charged him specifically with violating the neutrality provisions of the U.S. treaties with Great Britain, the Netherlands, and Prussia.212 The remaining counts charged him with violating the unwritten law of nations on neutrality by acts of hostility against Britain, the Netherlands, and Prussia, but these charges also noted the existence of the treaties that put the United States at peace with those countries.213

A panel of three judges—consisting of Wilson, Justice James Iredell, and Judge Richard Peters—deliberated on the legal issues and instructed the petit jury in a charge delivered by Wilson. Wilson told the jury: “It is the joint and unanimous opinion of the court, that the United States, being in a state of neutrality relative to the present war, the acts of hostility committed by Gideon Henfield are an offence against this country, and punishable by its laws.”214 He pointed both to the unwritten law of nations and to “positive laws, existing previous to the offence committed, and expressly declared to be part of the supreme law of the land,” noting that “[t]he constitution of the United States has declared that all treaties made, or to be made, under the authority of the United States, shall be part of the supreme law of the land.”215 As applicable to the case at issue, Wilson cited the first article of the Treaty of Amity with the Netherlands, the seventh article of the Treaty of Peace with Britain, and the first article of the Treaty of Amity with Prussia.216 “These treaties were in the most public, the most notorious existence, before the act for which the prisoner is indicted was committed.”217 Although Henfield was acquitted,218 the case illustrated the assumption that at least some treaty violations by individuals could be prosecuted even without a statute.219

In response to Henfield’s acquittal and those of other defendants,220 Congress passed the Neutrality Act, which specifically prohibited persons within the United States from accepting commissions from foreign states and enlisting in their service, as well as fitting out ships, augmenting their armaments, and launching military expeditions against foreign states with which the United States was at peace.221 In United States v. Arjona, the Supreme Court identified the 1794 Neutrality Act (and those of 1797, 1817, and 1818) as an exercise of Congress’s authority under the Offenses Clause.222 Some scholars have criticized this conclusion, arguing that “[i]nternational law did not prohibit private citizens from carrying contraband to belligerents, nor did it bar the service of a third-country national on belligerent privateers.”223 But Arjona’s conclusion seems more sound once we recognize that the Offenses Clause extends to treaties as well as the unwritten law of nations. The treaties that Henfield was alleged to have violated pledged peace not only between the United States and the states of Britain, the Netherlands, and Prussia, but also between the people of each.224 To be sure, the Neutrality Act went beyond implementation of these treaties by prohibiting persons in the United States from violating neutrality even where no treaty existed. But given that the Neutrality Act was a direct response to the acquittal in Henfield’s Case—a case that had specifically charged the defendant with violating treaties—it is reasonable to view that Act as at least in part an implementation under the Offenses Clause of U.S. treaty provisions pledging peace.

Congress’s actions from 1789 to 1794 thus suggest that it viewed the Offenses Clause as encompassing treaties. In the Judiciary Act of 1789, Congress exercised its authority under the Clause to authorize civil suits for torts in violation of “a treaty of the United States.”225 In the Crimes Act of 1790, Congress criminalized piracy and violations of safe-conducts, which corresponded to obligations in existing treaties.226 And in the Neutrality Act of 1794, Congress ensured that the Gideon Henfields of the future would not escape punishment if they violated treaties committing the United States to peace.227 It is worth noting that each of these exercises of the offenses power implemented both the unwritten law of nations and treaties. The ATS expressly mentions both, whereas the 1790 Crimes Act and the 1794 Neutrality Act encompassed treaty obligations but also went beyond them to define and punish what Congress understood to be violations of the unwritten law of nations. Implementing treaties and custom together made sense, for these two types of international law were often intertwined, just as they are today.

While treaties and custom often overlapped, so too did the constitutional authorities for implementing treaties. Early Congresses certainly did not believe that their authority to implement treaties was limited to the Offenses Clause. As Jean Galbraith has recently pointed out, congressional debate over the 1796 Jay Treaty focused on the Necessary and Proper Clause.228 So did debates over the 1815 commercial treaty with Great Britain.229 Because these treaties addressed numerous bilateral issues, the thrust of which was primarily commercial, the Offenses Clause would not have seemed as natural a fit as the treaty power together with the Necessary and Proper Clause or the Commerce Clause. But in the 1880s, when Congress looked to implement a treaty requiring its parties to enact legislation to punish violations and considered legislation to protect the treaty rights of aliens, it expressly invoked the Offenses Clause.

To understand Congress’s understanding of its own authority under the Offenses Clause during the late nineteenth century, it is best to begin with the legislative history of the 1884 Counterfeiting Act, which prohibited the counterfeiting of foreign government notes, bonds, and other securities.230 Although this Act did not implement a treaty, the House Report clearly described the offenses power in terms that comprehended treaties:

“The law of nations,” as used in this clause, is obviously what is now known among publicists as international law; in other words, what the Constitution termed the law of nations, or jus gentium, is now termed the jus inter gentes, or international law.

Whatever, therefore, may be regarded as an offense against the law which regulates the just relations between nations, may be defined and punished as an offense against the law of nations under [the Define and Punish] [C]lause of the Constitution.231

Congress thus described the law of nations as extending to all of “international law” and read the Offenses Clause as encompassing whatever “may be regarded as an offense against the law which regulates the just relations between nations.”232

Just a few years later, Congress acted on this understanding of the Offenses Clause, expressly invoking the Clause to support legislation to implement the Convention for the Protection of Submarine Cables,233 a multilateral treaty ratified by the United States in 1884. Article II of the Convention stated that “[t]he breaking or injury of a submarine cable . . . shall be a punishable offense,”234 while Article XII committed the parties “to take or to propose to their respective legislative bodies the measures necessary in order to secure the execution of this Convention, and especially in order to cause the punishment” of persons violating its provisions.235 To implement the Convention, Congress passed the Submarine Cable Act of 1888, sections 1 and 2 of which criminalized breaking submarine cables—legislation that is still in effect today.236 The bill was twice reported out of the House Committee on Foreign Affairs, and each report stated that the Offenses Clause and the Foreign Commerce Clause were sufficient to answer the question “whether or not Congress is empowered to pass this bill.”237

During this same period, both the Offenses Clause and the Necessary and Proper Clause were invoked as authority for proposed legislation protecting the treaty rights of aliens—legislation that ultimately failed to pass. From the 1880s through the turn of the century, violence and lynchings against resident aliens, particularly Italians and Chinese protected under treaties with the United States, were a cause of significant diplomatic concern, leading the executive and later Congress to seek to use federal criminal statutes to punish such crimes.238 The 1880 U.S. treaty with China, for example, provided that “[i]f Chinese . . . meet with ill treatment at the hands of any other persons, the Government of the United States will exert all its power to devise measures for their protection and to secure to them the same rights, privileges, immunities, and exemptions as may be enjoyed by the citizens or subjects of the most favored nation.”239 The Supreme Court had previously held in Baldwin v. Franks that existing federal statutes could not be construed to prohibit the conduct at issue.240 But the Court had emphasized that Congress clearly possessed the power to enact legislation protecting aliens’ treaty rights: “That the United States have power under the Constitution to provide for the punishment of those who are guilty of depriving Chinese subjects of any of the rights, privileges, immunities, or exemptions guarantied to them by this treaty we do not doubt.”241

An 1891 lynching in New Orleans brought renewed urgency to the topic.242 In his resulting address to Congress, President Harrison called for legislation “to make offenses against the treaty rights of foreigners domiciled in the United States cognizable in the Federal courts,” referring expressly to the United States’s “constitutional power to define and punish crimes against treaty rights.”243 In response, the Senate adopted a resolution directing the Foreign Relations Committee to propose legislation that would enable the United States “to use its constitutional power to define and punish crimes against treaty rights conferred upon such foreigners.”244 The Committee reported legislation that would have made it a federal crime to commit a violation of state law that also violated an alien’s rights under a treaty, and that would have enforced the penalties provided under state law.245 In the ensuing congressional debates, many parties agreed that Congress possessed constitutional authority to implement U.S. treaty commitments.246 At least one speaker expressly invoked the Necessary and Proper Clause,247 while another stated that Congress must carry out any punishment for acts committed against foreign citizens under its treaty obligations “in the only mode in which it can exercise the power committed to it by the Constitution, and that is by defining a crime and annexing a punishment.”248 The proposed legislation failed.249As a subsequent Senate report noted, “The chief ground of this opposition was not that Congress lacked power to so legislate, but that it was unnecessary to confer such jurisdiction on the United States courts, and, therefore, impolitic, because the prosecution of such offenses could be safely intrusted to the State courts.”250 Clearly, Congress’s view during the late nineteenth century was that the Offenses Clause, as well as other provisions of the Constitution, gave it authority to enact penal legislation required by a treaty or to protect rights guaranteed under a treaty.251

When Congress attempted to adopt anti-lynching civil rights legislation in the 1940s, it again looked to the Offenses Clause as a source of constitutional authority.252 In addition to the Fourteenth Amendment and the Republican Guarantee Clause,253 the House Report invoked “[t]he treaty power” and “the power to define and punish offenses against the law of nations” as authority for the legislation.254 The report pointed to U.S. treaty obligations under Articles 55 and 56 of the United Nations Charter to promote “universal respect for, and observance of, human rights . . . without distinction as to race, sex, language, or religion”255 and added that the same principle was reflected in “peace treaties with Italy, Rumania, Bulgaria, and Hungary containing guaranties that those countries would protect racial minorities in their midst from discrimination.”256 In light of these treaty obligations, the report concluded, “[c]learly we have here an adequate constitutional basis, either under the power to implement treaties or under the power to define offenses against international law, for a statute protecting all individuals against violence or threats of violence because of race or religion.”257

In passing the Foreign Sovereign Immunities Act (FSIA) in 1976,258 Congress again based its constitutional authority on the Offenses Clause, along with its authority to prescribe the jurisdiction of federal courts, the Foreign Commerce Clause, and the treaty power plus the Necessary and Proper Clause.259 The FSIA established rules governing the immunity of foreign states and their agencies and instrumentalities, U.S. jurisdiction over suits against foreign states and service of process, and attachment and execution against the property of foreign states to satisfy a judgment. Although most of these issues were not governed by international agreements,260 a few were. The FSIA therefore provides for service of process “in accordance with an applicable international convention on service of judicial documents.”261 With respect to execution of judgments, the FSIA made the immunity of government property subject not just to the exceptions stated in the Act262 but also to “existing international agreements to which the United States is a party.”263 As the legislative history explains, “[a] number of treaties of friendship, commerce and navigation concluded by the United States permit execution of judgments against foreign publicly owned or controlled enterprises.”264 So the FSIA is properly viewed as an implementation not only of customary international law and international comity, but also of certain treaty obligations.

Over the past three decades, Congress has acted repeatedly and expressly to implement treaties using its authority under the Offenses Clause. In 1984, Congress passed the Aircraft Sabotage Act265 “to implement fully the Convention for the Suppression of Unlawful Acts Against the Safety of Civil Aviation,”266 which required punishment of various acts of violence against aircraft, airports, or their personnel.267 Congress explained that such offenses under the Convention “gravely affect interstate and foreign commerce, and are offenses against the law of nations.”268 With respect to Congress’s authority, the Senate Report stated that the Act “is an exercise of the treaty power, of the power to regulate interstate and foreign commerce, and of the power to punish offenses against the laws of nations.”269

In 1992, Congress passed the Torture Victim Protection Act (TVPA), which created an express cause of action for civil damages for acts of torture and extrajudicial killing committed under color of foreign law.270 Congress stated that its purpose in adopting the TVPA was to “carry out the intent of the Convention Against Torture and Other Cruel, Inhuman or Degrading Treatment or Punishment,”271 and relied expressly on the Offenses Clause as a constitutional basis for the legislation.272 Congress explained the law as follows: “The [C]onvention [Against Torture] obligates state parties to adopt measures to ensure that torturers within their territories are held legally accountable for their acts. This legislation will do precisely that—by making sure that torturers and death squads will no longer have a safe haven in the United States.”273

It is clear that in providing a civil remedy for acts of torture, the statute was intended to implement the treaty—as Congress indicated—and not simply the prohibition against torture in customary international law. Article 4 of the Convention Against Torture mandates that states parties must make all acts of torture “punishable by appropriate penalties,”274 and although Article 4 mandates that this must include criminal penalties, it otherwise leaves the choice of penalties to individual States.275 Article 14 of the Convention further requires states parties to “ensure in its legal system that the victim of an act of torture obtains redress and has an enforceable right to fair and adequate compensation.”276 The United States adopted an understanding upon ratification that the Article 14 obligation applied only to torture committed in territory under a state’s jurisdiction,277 but Article 14 clearly permits states to go further and to provide a civil remedy for torture occurring elsewhere, as the TVPA did. Of course, the TVPA also implemented customary international law, particularly in its creation of a cause of action for extrajudicial killing,278 and Congress could have adopted a civil damages remedy against torturers to punish violations of the customary international law prohibition on torture even in the absence of the Convention. But this fact simply shows that treaties and customary international law are often intertwined today, just as they were at the Founding, and it highlights the problems with limiting the Offenses Clause to only one species of international law.

Congress expressly invoked the Offenses Clause again when it passed the War Crimes Act of 1996 to implement the grave breaches provisions of the Geneva Conventions. The original statute made it a federal crime for any U.S. national or servicemember to “commit[] a grave breach of the Geneva Conventions,” as defined in the four Geneva Conventions of 1949.279 The House Report stated that the Act was adopted “to carry out the international obligations of the United States under the Geneva Conventions [of 1949] to provide criminal penalties for certain war crimes,”280 noting that the Geneva Conventions required states parties to “enact appropriate implementing legislation criminalizing the commission of grave breaches.”281 Congress claimed constitutional authority for the legislation under the Offenses Clause, stating that “[t]he constitutional authority to enact federal criminal laws relating to the commission of war crimes is undoubtedly the same as the authority to create military commissions to prosecute perpetrators of these crimes.”282 Congress further pointed to the Supreme Court decisions in Yamashita and Quirin,283 which had upheld that authority under the Offenses Clause and construed the Clause as extending to treaties.284 When Congress amended the War Crimes Act in 1997, it again invoked the Offenses Clause.285

In 1998, Congress amended the Foreign Corrupt Practices Act (FCPA) to implement the OECD Convention on Combating Bribery of Foreign Public Officials in International Business Transactions, a multilateral treaty that was modeled on the FCPA but differed in a few respects. The sole and express purpose of the legislation was to implement the treaty.286 Most of the FCPA amendments fell squarely within the Foreign Commerce Clause, which was the authority for the original Act. But it was less clear that the commerce power would sustain the prohibition on unlawful payments that took place completely outside the United States. To implement this part of the Convention, Congress also invoked the Offenses Clause, stating that the exercise of “jurisdiction over U.S. businesses and nationals in furtherance of unlawful payments that take place wholly outside the United States” fell within Congress’s power to “define and punish * * * Offenses against the Law of Nations.”287

In the Military Commissions Act of 2006, Congress authorized the trial by military commission of “alien unprivileged enemy belligerents for violations of the law of war.”288 The House Armed Services Committee stated that the list of triable offenses “is based upon international treaties and U.S. criminal law” and reflects “the codification of the law of war into the United States Code pursuant to Congress’s constitutional authority to ‘Define and Punish * * * Offences against the Law of Nations.’”289 The report further noted that “[m]ost of the listed offenses constitute clear violations of the Geneva Conventions, the Hague Convention, or both,”290 that the definition of “unlawful enemy combatants” excluded persons recognized as “non-combatants under the Geneva Conventions,”291 and that in the view of Congress the commissions were a “regularly constituted court, . . . for purposes of common Article 3 of the Geneva Conventions.”292 Leaving aside the question whether Congress correctly interpreted international law for these purposes, the Act clearly reflects Congress’s view that the Offenses Clause authorized Congress to punish violations of international treaties governing armed conflict. The House Judiciary Committee found “the authority for this legislation in article 1, section 8 of the Constitution, including clauses 10 [the Offenses Clause], 11 [the Declare War Clause], 14 [the Rules for Armed Forces Clause] and 18 [the Necessary and Proper Clause].”293

Although this is not a comprehensive survey, the statutes discussed here are examples in which Congress has expressly invoked its authority under the Offenses Clause to implement U.S. treaty obligations. We note that Congress has passed a number of other statutes—specifically intended to implement treaties—for which the Offenses Clause would be a natural fit, including those punishing genocide,294 hostage taking,295 crimes involving foreign officials and internationally protected persons,296 terrorism financing,297 and nuclear materials,298 as well as the Chemical Weapons Convention Implementation Act,299 which is discussed further in Part IV.

It appears, then, that Congress has consistently understood its authority under the Offenses Clause to extend to the implementation of treaties. Some of the Acts discussed above have implemented a treaty alone, while others have defined and punished offenses under both treaties and customary international law. But Congress has rejected any artificial division between these different forms of international law. In the words of an 1884 House Report on Counterfeiting, “‘[t]he law of nations,’ as used in this clause, is obviously what is now known among publicists as international law.”300

Congress has also understood its authority to implement treaties under the Offenses Clause as one authority among many. It has therefore also invoked the Foreign Commerce Clause, the treaty power plus the Necessary and Proper Clause, and the power to establish lower federal courts, along with the Offenses Clause, in passing legislation to implement treaties. Congress’s view is thus consistent with the original understanding, discussed above, that the Offenses Clause is one piece of a constitutional package designed to comprehensively ensure that the United States could comply with its international obligations.

B. Supreme Court Precedent

As discussed above, through at least the first third of the nineteenth century, the U.S. Supreme Court consistently regarded the law of nations as including a “conventional law of nations” consisting of treaties.301 Furthermore, although the Court has considered the Offenses Clause only a few times, its decisions also support the conclusion that treaties fall within the scope of the Clause. The Court has treated the Clause as a source of congressional power to implement international law generally in passing upon laws prohibiting counterfeiting, protecting embassies, and establishing military tribunals, among others.302 In so doing, the Court has emphasized the overarching purposes of the Clause to allow Congress to punish violations of international law and to meet the international commitments of the United States. The Court has not attempted to distinguish carefully between rules of customary international law and rules that are treaty-based, but has drawn from either source, as appropriate for the context. In short, the Court has looked generally to international law—which encompasses both treaties and customary international law—as the modern referent for the “law of nations.” At times, the Court has specifically applied the Offenses Clause to uphold statutes implementing treaties. On other occasions, the Court has appeared to construe the Clause quite broadly as allowing the prohibition of any conduct that could give rise to state responsibility or harm U.S. relations with foreign states.

At the most general level, the Court has cited the Offenses Clause as evidence of the Constitution’s purpose of giving the federal government control over matters of international law and foreign relations. In Fong Yue Ting v. United States, for example, the Court observed that “[t]he United States are a sovereign and independent nation, and are vested by the constitution with the entire control of international relations, and with all the powers of government necessary to maintain that control, and to make it effective,” citing the Offenses Clause as an example.303

More specifically, the Supreme Court’s decisions emphasize that the purpose of the Offenses Clause is to enable the United States to comply with its international commitments, a purpose that applies equally to treaties and to customary international law. In United States v. Arjona,304 the Court considered the constitutionality of the 1884 Counterfeiting Act, which criminalized the counterfeiting of foreign securities.305 As discussed above, Congress had invoked the Offenses Clause as the constitutional authority for adopting the Act.306 The Court noted that the Constitution makes the national government “responsible to foreign nations for all violations by the United States of their international obligations, and because of this congress is expressly authorized ‘to define and punish . . . offenses against the law of nations.’”307 No treaty obligation was at issue in Arjona, but the Court relied on Vattel to establish that “the obligation of one nation to punish those who, within its own jurisdiction, counterfeit the money of another nation has long been recognized,”308 an obligation the Court concluded should be extended to foreign securities.309 The Court emphasized that “the United States must have the power to pass [such a law] and enforce it themselves, or be unable to perform a duty which they may owe to another nation, and which the law of nations has imposed on them as part of their international obligations.”310 Consequently, the Court concluded, “if the thing made punishable is one which the United States are required by their international obligations to use due diligence to prevent, it is an offense against the law of nations.”311 This definition of the scope of the Offenses Clause, as applying to any acts which the United States has an “international obligation” to prevent, would readily include treaties.312

The same day that Arjona was decided, the Supreme Court decided Baldwin v. Franks, in which the Court confirmed that Congress had authority to create federal criminal remedies for attacks on aliens whose rights were protected by treaty.313 There is no question that the rights at issue in that case were treaty-based, and the brief on behalf of the United States Marshal relied substantially on an Offenses Clause theory.314 Although the Supreme Court did not specify the constitutional basis for the power to punish treaty violations that it recognized, the decisions in these two cases support the view that the Court did not consider the Offenses Clause authority to be limited to customary international law.315

A century later, the Supreme Court reiterated Arjona’s approach in Boos v. Barry.316 At issue in Boos was the constitutionality of a provision of the District of Columbia Code, which prohibited the display of signs that offended the dignity of embassies and prohibited assembly within 500 feet of an embassy.317 The Court indicated that Congress had enacted the provision in 1938 “pursuant to its authority under Article I, § 8, cl. 10, of the Constitution to ‘define and punish . . . Offenses against the Law of Nations.’”318 Ultimately the Court avoided the issue of constitutional authority to enact the provision, holding that the display clause was not narrowly tailored to serve the government’s interests319 and upholding the assembly provision based on a narrowing construction.320

In the course of its opinion, however, the Court elaborated on the purpose of the Offenses Clause:

As a general proposition, it is of course correct that the United States has a vital national interest in complying with international law. The Constitution itself attempts to further this interest by expressly authorizing Congress “[t]o define and punish Piracies and Felonies committed on the high Seas, and Offenses against the Law of Nations.”321

The Court observed that the D.C. law was most strongly supported by the dignity interest protected by Article 22 of the Vienna Convention on Diplomatic Relations, “which all parties agree represents the current state of international law.”322 The Vienna Convention, which entered into force in 1964, was adopted largely to codify customary international law concerning diplomats.323 Although the Court discussed the United States’s interest in enacting the law in terms of “international law” and “international relations,” it did not attempt to distinguish between customary international law and the Convention.324 Moreover, the United States’s “vital national interest in complying with international law”—the interest that “[t]he Constitution itself attempts to further” through the Offenses Clause—plainly applies not just to customary international law but also to treaties.

While Arjona and Boos articulate purposes for the Offenses Clause that are consistent with encompassing treaties, the Supreme Court’s military commission cases furnish specific examples of decisions construing the Offenses Clause to reach treaties. The first such case was Ex parte Quirin,325 in which the Court held that German saboteurs captured in the United States were properly tried by military commission under the 1920 Articles of War.326 In enacting Article 15 referring to military commissions, the Court reasoned, Congress had

exercised its authority to define and punish offenses against the law of nations by sanctioning, within constitutional limitations, the jurisdiction of military commissions to try persons for offenses which, according to the rules and precepts of the law of nations, and more particularly the law of war, are cognizable by such tribunals.327

The Court did not view the “law of nations” in this context as limited exclusively to customary international law. The Court defined the law of war “as including that part of the law of nations which prescribes, for the conduct of war, the status, rights and duties of enemy nations as well as of enemy individuals,”328 and it relied expressly on the definition of “belligerent” in the Fourth Hague Convention of 1907.329 That Convention “recognized that there is a class of unlawful belligerents” not entitled to treatment as prisoners of war and “by Article 15 of the Articles of War Congress has made provision for their trial and punishment by military commission, according to ‘the law of war.’”330

In Application of Yamashita, the Court confirmed the jurisdiction of a military commission to try the commanding general of the Japanese army in the Philippines for failing to prevent atrocities by troops under his command.331 The Court reiterated its conclusion in Quirin that Article 15 was an exercise of Congress’s power under the Offenses Clause332 and that Congress had “adopted the system of military common law applied by military tribunals[,] . . . as further defined and supplemented by the Hague Convention, to which the United States and the Axis powers were parties.”333 The Court also looked to other articles of the Fourth Hague Convention as establishing the law of nations with respect to protection of civilians in occupied territory, and to the Fourth and Tenth Hague Conventions and the Geneva Red Cross Convention of 1929 for a commander’s responsibility for violations by his forces.334 The Court concluded that the principle of command responsibility established by these treaties could be applied by military commissions created by Congress under the Offenses Clause to punish violations of the laws of war. Yamashita thus confirms that the Court considered the law of war—part of the law of nations—to include treaties.

In 1950, Congress replaced the Articles of War with the Uniform Code of Military Justice (UCMJ), but Article 15 was carried over as Article 21 of the UCMJ.335 In Hamdan v. Rumsfeld,336 the Supreme Court struck down the system of military commissions established by President Bush in 2001.337 The Court found that the commissions violated the Geneva Conventions and therefore failed to comply with the statutory mandate that commissions comply with the laws of war.338 The Court observed that “the ‘rules and precepts of the law of nations’—includ[e],inter alia, the four Geneva Conventions signed in 1949”339 and concluded that the commissions could not be considered “regularly constituted court[s]” within the meaning of Common Article 3 of the Geneva Conventions.340 Writing for four members of the Court, Justice Stevens further concluded that the charge of conspiracy was not clearly a violation of the law of nations and that Congress had not “in exercise of its constitutional authority to ‘define and punish . . . Offences against the Law of Nations,’ U.S. Const., Art. I, § 8, cl. 10, positively identified ‘conspiracy’ as a war crime.”341 He noted that “none of the major treaties governing the law of war identifies conspiracy as a violation thereof.”342 In other words, the most recent word from the Court on the Offenses Clause confirms—consistent with Quirin and Yamashita—that Congress may punish offenses “defined by . . . treaty” by exercising its power under the Offenses Clause.

The Supreme Court’s military commission cases also demonstrate that Congress’s authority under the Offenses Clause is not limited to passing legislation that a treaty obligates it to adopt. Although the Geneva Conventions do obligate the United States to punish war crimes,343 no treaty requires the United States to use military commissions for this purpose. In sustaining the use of military commissions to punish violations of the law of war—including violations of treaties—the Supreme Court has acknowledged that Congress enjoys some discretion under the Offenses Clause in determining how to punish violations of the law of nations, a point to which we return in Part IV.

In sum, the Supreme Court’s precedents are fully consistent with the reading of the Offenses Clause advanced here. The Court has repeatedly pointed to the Clause as evidence of the Framers’ intent to confer authority on the federal government over questions of international law and foreign relations. It has stressed that the purpose of the Clause is to allow Congress to ensure compliance with the United States’s international commitments. Finally, in the military commission cases, it has expressly construed Congress’s power under the Offenses Clause to implement treaties defining the laws of war. The Court’s decisions are consistent with the original understanding of the Clause discussed above.344 And its approach is sensible given the increased importance of treaties and their interrelationship with customary international law in the modern era.

III. the significance of treaties in modern international law

International law has changed dramatically since the Offenses Clause was adopted. Over the course of the nineteenth century, international law came to be seen in positivist terms.345 Vattel’s categories of the law of nations based on natural law—the necessary and the voluntary law of nations346—fell away, leaving an international law that consisted only of treaties and customary international law based on state practice. Modern customary international law differs from Vattel’s “customary law of nations” in that a general and consistent practice of states, taken under a sense of legal obligation, is now understood to give rise to universally binding rules from which nations are not free to withdraw.347 The law of treaties has remained largely the same, but treaties are no longer commonly referred to as the “conventional law of nations.”348 Instead, “international law” became the modern concept that encompasses both treaties and customary international law. Partly as a result of these changes, the original understanding that the “law of nations” included violations of treaties was largely lost.

Other changes in international law, however, may have made the Offenses Clause’s embrace of treaties even more important. Although treaties have been intertwined with customary international law from the beginning of the Republic,349 the significance of treaties as a form of international lawmaking has dramatically increased in modern times. As the Restatement (Third) of Foreign Relations Law observes, “In our day, treaties have become the principle vehicle for making law for the international system; more and more of established customary law is being codified by general agreements.”350 The nineteenth-century impulse towards codification led to an increase in the number of treaties designed both to create new obligations and to restate, clarify, and further elaborate upon existing obligations under customary international law. Particularly in the period since World War II, customary international law has increasingly been codified into multilateral international conventions, including through the activity of the International Law Commission, which was established by the U.N. General Assembly in 1948 for the explicit purposes of codifying international law and contributing to its progressive development. A reading of the Offenses Clause as limited to customary international law would not only create difficult line-drawing problems but would also undercut the purpose of the Clause to facilitate U.S. compliance with international law.

A comprehensive consideration of codification and progressive development is beyond the scope of this Article, but we offer a few examples that seem particularly relevant to Congress’s authority under the Offenses Clause. As noted above, although the crime of piracy was defined by the unwritten law of nations at the Founding,351 piracy has since been codified by the Convention on the High Seas352 and by the United Nations Convention on the Law of the Sea (UNCLOS).353 With some exceptions, both conventions were largely intended to codify customary international law354 and are generally regarded as having done so, including with respect to piracy.355 The United States has ratified the Convention on the High Seas, and while it has not yet ratified the UNCLOS, the United States regards most of its provisions as restatements of customary international law.356

The protection of ambassadors and other public ministers under the Offenses Clause also dates back to the First Congress.357 While the rights of such officials were then based in the unwritten law of nations, they have been codified and developed by the 1961 Vienna Convention on Diplomatic Relations (VCDR),358 the 1963 Vienna Convention on Consular Relations (VCCR),359 and the 1973 Convention on the Prevention and Punishment of Crimes Against Internationally Protected Persons, Including Diplomatic Agents.360 Various provisions of the U.S. Code now implement these treaty obligations to prohibit violence against foreign officials.361 Given the clear purpose of the Offenses Clause to allow Congress to punish violations of U.S. international law commitments, it makes little sense to think that Congress’s authority to protect ambassadors and other public ministers under the Offenses Clause is limited to the customary international law obligations that have been subsumed and further developed by these treaties.

The post-World War II era has seen the rise of human rights treaties that partially codify customary international law and that have contributed to the development of customary law, such as the Convention Against Torture, the Genocide Convention, and the major multilateral human rights treaties. Congress has implemented the Genocide Convention and the Convention Against Torture by, inter alia, adopting criminal statutes362 as well as providing for civil liability.363 Although the Genocide Convention perhaps preceded the recognition of genocide as a customary norm, each of these treaties now represents, at least to some extent, a codification of customary international law.364 It would be odd to conclude that the Offenses Clause does not authorize Congress to implement the more detailed provisions of the Genocide and Torture Conventions, but only the customary international law principles reflected in those conventions.

Similarly, prior to the twentieth century, much of the law of war was unwritten.365 Now most of the law of armed conflict is treaty-based, at least for international armed conflicts, particularly through the 1907 Hague Conventions and the 1949 Geneva Conventions and their additional protocols, which reflect a mixture of customary and conventional law.366 As previously noted, Congress has exercised its authority under the Offenses Clause to criminalize grave breaches of the Geneva Conventions,367 and the Supreme Court has pointed to other treaties as the basis for Congress’s authorization of military commissions.368 These are just a few examples of the diverse ways in which the relationship between treaties and customary international law has become more complex and intertwined.

It is also important to recall that the United States often agrees by treaty to punish individual conduct that does not violate customary international law—like damaging submarine cables, bribing foreign officials, or financing terrorism.369 As a matter of international law, the United States is no less bound to comply with these treaty commitments than when the conduct condemned in the treaty is also prohibited by customary international law.370 Given that a principal purpose of the Offenses Clause is to enable the United States to comply with its international commitments, it makes little sense to distinguish obligations that are tied in some way to customary international law from those that rest on a treaty alone.

In short, while changes in international law since the adoption of the Constitution may have obscured the meaning of the phrase “law of nations” in the Offenses Clause, they have also made it even more important to recapture the original understanding of that phrase as encompassing treaties. The United States’s international obligations are increasingly treaty-based. Those treaties often build on a foundation of customary international law. It is frequently difficult to determine which treaty provisions codify existing customary international law and which impose additional obligations, particularly since codification itself can contribute to the further development of customary international law. An interpretation of the Offenses Clause that authorizes Congress to implement unwritten customary international law but not treaties is artificial and unworkable when these two sources of international law are so deeply entwined.

If the Offenses Clause were in fact limited to customary international law, then treaties could be invoked as a basis for congressional authority under the Offenses Clause only to the extent that they reflected custom. But it is simply implausible to conclude that Congress could exercise authority under the Offenses Clause to punish assaults against ambassadors when the protection of diplomats under international law rested exclusively on custom, but could not implement the Vienna Convention on Diplomatic Relations under the same authority, or could do so only to the extent that the treaty did not alter customary international law. Nor would such an approach be consistent with the constitutional design.

Fortunately, the historical record shows that this is not how the Offenses Clause has been understood and applied over time. The Clause instead has always been understood as giving Congress a basis for enforcing international law—including complying with the United States’s international law obligations and domestically punishing violations of international law—whether based upon treaties, customary international law, or both. Neither Congress in adopting legislation under the Offenses Clause, nor the Supreme Court in evaluating and enforcing such legislation, has drawn bright lines to limit application of the Clause to U.S. customary international law obligations. On the contrary, the practice throughout the nation’s history—consistent with the original understanding—has been to construe and apply the Clause in terms that embrace both treaties and unwritten international law.

IV. implications for implementing legislation

Recognizing that the Offenses Clause allows Congress to define and punish offenses under treaties leaves open important questions regarding the scope of that authority. Some limiting principles are internal to the Offenses Clause itself. For example, in order for Congress to punish an “Offence[] against the Law of Nations,” the conduct being punished must be proscribed by international law; punishment may not be imposed simply to advance international relations. These internal limiting principles, and the discretion Congress enjoys under the Offenses Clause, are the subject of this Part. Other limiting principles are external to the Offenses Clause. For example, under the First Amendment, legislation implementing a treaty may not impose content-based restrictions on speech unless necessary to serve a compelling state interest.371 While we will refer to some of these external limitations in passing, a full consideration of such limitations is beyond the scope of this Article.

With respect to internal limiting principles, we believe—and historical practice suggests—that the Offenses Clause allows Congress to adopt civil or criminal legislation in at least the following circumstances: (1) a treaty operates directly on individuals to prohibit the conduct; (2) a treaty requires domestic legislation punishing the conduct; (3) a treaty clearly proscribes the conduct, even if it does not operate directly on individuals or expressly mandate punishment; and (4) a treaty authorizes punishment of the conduct, even if it does not require it.

These four categories include not only treaties that require the United States to punish conduct, but also treaties that authorize the United States to punish conduct without requiring it to do so. The first is uncontroversial. In United States v.Arjona, the Supreme Court confirmed that the Offenses Clause gave Congress, at a minimum, the power to punish conduct that could give rise to state responsibility, holding that “if the thing made punishable is one which the United States are required by their international obligations to use due diligence to prevent, it is an offense against the law of nations.”372 The state responsibility reading of Arjona and the scope of the Offenses Clause has been adopted by scholars ranging from Jack Goldsmith to Louis Henkin.373 But there is also historical support for the view that the Clause permits Congress to address conduct that international law authorizes, but does not require, states to punish. A traditional example is piracy. Although condemned under international law, piracy was not an act that states were required to punish under all circumstances. Pirates were hostis humani generis, and states were authorized by international law, but not obligated, to punish them wherever they were found.374 This remains true today under operative treaties.375 Nevertheless, piracy has long been prohibited by international law and recognized as a violation of the law of nations that the United States could punish under either the piracy prong of Article I, Section 8, Clause 10, or the Offenses Clause.376 A modern example is the United Nations Convention Against Illicit Traffic in Narcotic Drugs and Psychotropic Substances, which authorizes but does not require the punishment of narcotics offenses in certain situations, including offenses committed within the territorial waters of another nation.377

Some authority goes even further, suggesting that Congress may punish under the Offenses Clause any conduct that gives offense to foreign nations and thus interferes with the foreign relations of the United States. In 1833, Justice Story described the Clause as giving Congress “the power to define and punish all such offences, which may interrupt our intercourse and harmony with, and our duties to [foreign nations].”378 There are also broad dicta in Arjona that could be understood to allow Congress to punish any conduct that could cause annoyance to a foreign state.379 We believe this suggestion goes too far. The text of the Offenses Clause requires that the punishable conduct be an “Offence[] against the Law of Nations,”380 not an “Offence to a foreign nation.” The fact that conduct may interfere with foreign relations does not, by itself, satisfy that requirement. International law must proscribe the conduct.

Finally, Congress enjoys considerable discretion under the Offenses Clause to define offenses under customary international law and treaties. But as we discuss below, Congress may not create or recategorize offenses without support from international law. Congress also has discretion in punishing such offenses to choose a means rationally related to what is required or authorized by international law. In addition, Congress’s discretion is subject to whatever other limitations international law or the U.S. Constitution might impose.381

A. Four Categories of Treaties

For purposes of exposition, we identify four categories of treaties that, in our view, provide the basis for Congress to exercise its authority under the Offenses Clause. In reality, treaty commitments come in many variations, and it may be more accurate to think of them as spanning a spectrum from those that directly prohibit individual conduct to those that proscribe conduct and authorize, but do not require, punishment.

1. Treaties That Directly Prohibit Conduct by Individuals

In this category, the treaty itself creates international law obligations not simply for states, but for individuals directly. The operation of treaties in this category is analogous to the operation of certain customary international law rules on individuals—like the prohibition against piracy historically and the prohibition against torture today. When a treaty operates directly on individuals, the Offenses Clause allows Congress to define the conduct more specifically, if necessary, as well as to establish the appropriate punishment.

The neutrality provisions at issue in Henfield’s Case could be characterized as falling into this group—at least as they were understood by the Washington Administration.382 Treaties that would truly satisfy this category are, however, rare in U.S. practice. Different legal systems have different ways of incorporating treaties into their domestic laws. In the United States, it has been generally accepted that a self-executing treaty ordinarily cannot be the basis for a criminal prosecution, and that a statute is required to create a criminal offense.383 As a result, the United States generally does not negotiate treaties that operate directly on individuals where criminal punishment is contemplated.

2. Treaties That Require Domestic Legislation Punishing Conduct

Many treaties throughout U.S. history have mandated that states parties adopt penal legislation. Sometimes the treaty imposes an obligation to punish conduct that is already an offense under customary international law. Sometimes the treaty both codifies and develops an offense under international law, while adding an obligation to punish the offense. Often a treaty proscribes conduct that does not violate customary international law and requires a state to punish that conduct.

The Convention Against Torture is perhaps the clearest example of a treaty that requires states parties to punish conduct already prohibited by customary international law. With respect to torture that meets the Convention’s definition,384 each state is required to “ensure that all acts of torture are offences under its criminal law”385 and “punishable by appropriate penalties.”386 The United States implemented these obligations by adopting criminal legislation addressing extraterritorial acts of torture387 and by enacting the TVPA.388 Although the civil remedies available under the TVPA are broader than the understanding the United States adopted at the time of ratification,389 the TVPA’s creation of a civil damages remedy against perpetrators, in addition to the establishment of criminal remedies, is entirely consistent with the Article 4(2) obligation to make torture “punishable by appropriate penalties.”390

Other treaties—like the Genocide Convention and the Geneva Conventions—both codify and develop customary international law, while adding a treaty obligation to punish the conduct. Article I of the Genocide Convention, for example, “confirm[s] that genocide, whether committed in time of peace or in time of war, is a crime under international law which [states parties] undertake to prevent and to punish.”391 Articles II and III define genocide and related punishable acts, while Article V commits states parties “to enact, in accordance with their respective Constitutions, the necessary legislation to give effect to the provisions of the present Convention and, in particular, to provide effective penalties for persons guilty of genocide or of any of the other acts enumerated in article III.”392 Congress met this obligation, inter alia, by passing the Genocide Convention Implementation Act.393

Still other treaties require the states parties to prohibit individual conduct that does not otherwise violate international law. Thus, the 1884 Convention for the Protection of Submarine Telegraph Cables,394 which Congress implemented via the Offenses Clause, identified the punishable offense and mandated the adoption of any necessary legislation “to cause the punishment” of violators.395 The 1973 Convention for the Suppression of Unlawful Acts Against the Safety of Civil Aviation,396 which Congress also implemented through the Offenses Clause,397 specifies the conduct to be prohibited and mandates that states parties “make the offenses mentioned . . . punishable by severe penalties.”398 Numerous other treaties follow this format, including conventions on aircraft sabotage, hostage taking, counterterrorism, and biological or nuclear weapons—a number of which Congress has explicitly enforced through the Offenses Clause.399

The Chemical Weapons Convention, which was at issue in Bond v. United States,400 also requires the prohibition of individual conduct that does not otherwise violate international law. Article VII(1)(a) of the Convention obligates the United States to “[p]rohibit natural and legal persons . . . from undertaking any activity prohibited to a State Party under this Convention, including enacting penal legislation with respect to such activity.”401 The Convention defines chemical weapons and prohibits their development, acquisition, or use.402 The Chemical Weapons Convention Implementation Act adopted by Congress closely tracks these provisions.403 In Bond, the Supreme Court did not address the constitutional basis for the Act, holding instead that the Act did not reach “purely local crimes” in the absence of a clear indication that Congress meant to do so.404 Our reading of the Offenses Clause provides a clear constitutional basis for the Act, in addition to Congress’s authority under the Commerce Clause and the Article II Treaty Clause coupled with the Necessary and Proper Clause.405 However, by grounding the act directly in an Article I power, our reading also avoids the potential problems that Justice Scalia saw in combining the Necessary and Proper Clause with the Article II treaty power.406

3. Treaties That Mandate Certain Conduct but Do Not Expressly Require Punishment for Violations

Treaties in this category impose obligations on the United States that individual conduct may violate, but they do not specifically require that a state party adopt penalties for their violation. Punishing conduct contrary to such obligations is fully consistent with the purposes of the Offenses Clause, including the Court’s approach in Arjona, since the treaties impose an international legal obligation on the United States to secure compliance.

For example, Article 36 of the Vienna Convention on Consular Relations obligates states parties to inform any detained national of a foreign state party of his right to have his consulate notified of his detention.407 Although the Convention does not obligate states parties to punish individual violations of these requirements or otherwise expressly address the issue of remedies, the Convention does mandate that “the laws and regulations of the receiving state . . . must enable full effect to be given” to the obligations under the Article.408 The Offenses Clause therefore would seem fairly to encompass the imposition of civil or criminal penalties for violations of this obligation.409

The treaty obligations that formed the basis for the proposed legislation protecting aliens against violence in the 1880s and 1900s fall into this category. Treaties such as the 1880 U.S.-China Treaty pledged that if nationals of the foreign state residing in the United States “meet with ill treatment at the hands of any other persons, the Government of the United States will exert all its power to devise measures for their protection and to secure to them the same rights, privileges, immunities, and exemptions as may be enjoyed by the citizens or subjects of the most favored nation.”410 Although the treaties did not require any specific legislation to accomplish this end, either the federal conspiracy statutes at issue in Baldwin or the later proposed statute establishing federal jurisdiction over crimes violating alien treaty rights would have been reasonable measures for Congress to adopt under the Offenses Clause in order to secure compliance with the treaty.411

A final example is the statute regulating embassy protests, which was at issue in Boos v. Barry.412 Article 22(2) of the Vienna Convention on Diplomatic Relations provides that the receiving state “is under a special duty to take all appropriate steps to protect the premises of the mission against any intrusion or damage and to prevent any disturbance of the peace of the mission or impairment of its dignity.”413 The United States maintained that the relevant legislation constituted “appropriate steps” to secure this obligation,414 although the Supreme Court was unconvinced that the act was sufficiently tailored to the international legal obligation. The D.C. Circuit, on the other hand, had upheld the legislation as a valid exercise of the Offenses Clause, which “authorized Congress to derive from the often broadly phrased principles of international law a more precise code, as it determined that to be necessary to bring the United States into compliance with rules governing the international community.”415 The Court of Appeals appears to be correct, so far as the analysis goes. The very generally worded Article 22(2) obligation to “prevent any disturbance of the peace of the mission” and any “impairment of its dignity” clearly affords Congress some discretion in deciding what legislation is appropriate under the Offenses Clause to comply with the United States’s international obligations.416Congress had also exercised that authority by adopting other, more narrowly tailored legislation protecting consular premises. But such a generally worded treaty obligation nevertheless may not provide the compelling government interest necessary to overcome First Amendment concerns, as the Boos Court recognized.417

4. Treaties That Authorize Punishment of Certain Conduct

In some cases, although a treaty proscribes certain conduct, it does not mandate enforcement in a particular context, but instead establishes international law authority to punish where such authority would not otherwise exist under international law. Such examples often involve international agreements that override customary international law rules of jurisdiction, which would otherwise limit a state’s authority to prescribe conduct and enforce its law outside its own territory.418 Positive international law, however, can overcome such jurisdictional barriers, whether in the form of the consent of the foreign state or a Security Council resolution.

For example, the UN Convention Against Illicit Traffic in Narcotic Drugs and Psychotropic Substances, which the United States ratified in 1990, was adopted for the purpose of “promot[ing] co-operation . . . [to] address more effectively . . . illicit traffic in narcotic drugs and psychotropic substances having an international dimension.”419 The Convention expressly admonishes states to comply with the Convention “consistent with the . . . territorial integrity of States.”420 The Convention specifies in detail a range of drug-related offenses, and Article 3 declares that each state party “shall adopt such measures as may be necessary to establish [such acts] as criminal offences under its domestic law.”421 With respect to prosecution, Article 4 then distinguishes two groups of cases. First, it provides that states parties “[s]hall”establish criminal jurisdiction over drug offenses committed within their territory or on state-registered vessels or aircraft.422 Second, it provides that states parties “may” assert criminal jurisdiction over the relevant offenses if committed by a national or resident of the state or if committed in relation to an offense within the territory of the state, or over conduct on a foreign vessel outside the state’s territory based on an agreement with another state party.423 In the first group of cases, the Convention mandates punishment, and thus falls into category two above. In the second group of cases, the Convention authorizes, but does not require, the exercise of criminal jurisdiction. Article 17 further provides that “[t]he Parties shall co-operate to the fullest extent possible to suppress illicit traffic by sea, in conformity with the international law of the sea,”424 and contemplates bilateral or regional agreements to authorize enforcement activity that would otherwise violate international law.425

Pursuant to this regime, the United States has entered approximately two dozen bilateral agreements with foreign states authorizing the United States to exercise criminal jurisdiction over drug trafficking activity in a foreign state’s territorial waters with the consent of the foreign state. For example, the United States has entered into an agreement with Panama providing that Panama may “waive its right to exercise jurisdiction and authorize the enforcement of the other Party’s law against the vessel, cargo and/or persons on board.”426 In 1986, in anticipation of the Narcotics Convention, Congress established a statutory basis for exercising such extraterritorial jurisdiction, the Maritime Drug Law Enforcement Act (“MDLEA”), which criminalizes drug trafficking on “a vessel subject to the jurisdiction of the United States,”427 including “a vessel in the territorial waters of a foreign nation if the nation consents to the enforcement of United States law by the United States.”428

Under this treaty regime, the United States has a legal obligation to cooperate in the suppression of illicit drug-trafficking activity; a legal obligation to punish specified drug trafficking activity that occurs in its territory or on its vessels or aircraft; and authority under the Convention to punish the same specified conduct if committed by a U.S. national or, pursuant to an appropriate agreement, in the territorial waters of another state party.429

If the Offenses Clause authorizes Congress to punish only conduct that the United States is obligated by international law to prohibit, it is not clear that the Clause would allow Congress to implement all of the provisions of the MDLEA. The United States has no specific international legal obligation to exercise criminal jurisdiction over drug trafficking activity by its nationals or in foreign territorial waters.430 The vagueness of the Article 17 obligation to “co-operate to the fullest extent possible to suppress illicit traffic by sea” would provide a rather tenuous basis for legislation under the Offenses Clause.

In United States v. Bellaizac-Hurtado,431 the Eleventh Circuit held that the MDLEA exceeded Congress’s power under the Offenses Clause because drug trafficking was not prohibited by the law of nations, which the court misunderstood as limited to customary international law.432 Of course, the statute could also be understood as an exercise of Congress’s constitutional authority under the treaty power and the Felonies Clause, each coupled with the Necessary and Proper Clause.433 But we believe that the statute in that case should have been upheld under the Offenses Clause because the treaty proscribed trafficking and authorized its punishment.

Similarly, in an effort to strengthen global efforts to suppress piracy in the Gulf of Aden, the UN Security Council has adopted a number of resolutions authorizing states to exercise jurisdiction over acts of piracy beyond what would be traditionally allowable under international law. Specifically, since 2008, the Security Council, with Somalia’s consent, has authorized states to conduct counter-piracy operations in the territorial waters of Somalia—operations that they otherwise would be authorized to conduct only on the high seas.434 The Security Council has made clear that this particular authorization is specific to Somalia and does not purport to establish a new rule of customary international law.435 These authorities have been renewed and strengthened over time. The Security Council has further called upon states to exercise robust enforcement authority in the Somali piracy context. For example, in 2011 resolutions, the Security Council urged “States to favourably consider the prosecution of suspected, and imprisonment of convicted, pirates apprehended off the coast of Somalia,”436 and “[r]ecognize[d] the need to investigate and prosecute not only suspects captured at sea, but also anyone who incites or intentionally facilitates piracy operations, including key figures of criminal networks involved in piracy who illicitly plan, organize, facilitate, or finance and profit from such attacks.”437 The authority established by Resolution 1816 to exercise traditional authorities over piracy in Somali territorial waters is binding on the United States under the UN Charter,438 and thus establishes international legal authority—but not an obligation—to prosecute and punish piracy there.

In our view, Congress’s authority under the Offenses Clause should properly extend to treaties that authorize the punishment of specifically defined individual conduct, even if they do not require punishment of that conduct. As noted above, one of the paradigm offenses under the Clause was piracy, which international law authorized, but did not require, states to punish.439 Moreover, treaty negotiations are often complex and must take into consideration a range of international and domestic considerations. Sometimes the states parties may wish to reserve discretion about whether to prohibit conduct in particular situations. To insist that Congress may exercise its authority under the Offenses Clause only when a treaty has obligated the United States to act would be to adopt an unrealistic view of the way that treaties are negotiated and potentially to hamstring U.S. negotiators by limiting their range of options.

B. Congress’s Discretion Under the Offenses Clause

Congress necessarily enjoys some discretion in determining how to define and punish conduct in the course of honoring the United States’s international legal commitments,440 but this discretion is not boundless. Here we find it useful to distinguish the deference owed to Congress’s definition of the offense from the deference owed to its choice of the means for punishment.

The word “define” strongly suggests that Congress lacks authority under the Offenses Clause to create new violations of the law of nations out of whole cloth.441 In the early years of the Republic, one question was whether Congress could punish anything it wished on the high seas simply by calling it piracy.442 Just a few years after ratification of the Constitution, Justice James Wilson expressed in a grand-jury charge his doubt that murder on the high seas could be considered piracy “consistently with the predominant authority of the law of nations.”443 Three decades later, the Supreme Court held in United States v. Furlong that Congress could not punish simple murder as piracy.444 If Congress were allowed to do so, the Court reasoned, “what offence might not be brought within their power by the same device?”445 In Arjona, the Court reiterated that “[w]hether the offense as defined is an offense against the law of nations depends on the thing done, not on any declaration to that effect by congress.”446

Definition of the offense is often less difficult with treaties than with customary international law. To be sure, some treaty provisions require further definition before they are incorporated into a domestic criminal code, like the neutrality provisions of early U.S. treaties implemented by the Neutrality Act447 or Article 22(2) of the Vienna Convention on Diplomatic Relations, which imposed a duty on the United States “to prevent any disturbance of the peace of the mission or impairment of its dignity.”448 But most modern treaties—particularly those that authorize or require the United States to punish conduct—define the prohibited conduct with great specificity. The Genocide Convention, for example, provides a detailed definition of genocide,449 which the U.S. implementing legislation tracks quite closely.450

Turning to the means of punishment, some treaties limit Congress’s discretion by requiring particular kinds of legislation. The Convention Against Torture and the UN Convention Against Illicit Traffic in Narcotic Drugs and Psychotropic Substances, for example, require the United States to make certain conduct a “criminal” offense.451 The Chemical Weapons Convention, on the other hand, requires the United States to prohibit certain conduct through “penal legislation,”452 an obligation that Congress presumably could have satisfied by adopting civil penalties.

In the absence of specific limitations in the treaty, and in the absence of constitutional limitations external to the Offenses Clause,453 we think Congress has authority under the Offenses Clause to adopt any mode of punishment that is rationally related to enforcing the treaty. We draw this rational relationship test from cases interpreting the Necessary and Proper Clause,454 but we believe it is appropriate to do so for two reasons. First, the Supreme Court has applied a similarly deferential test to Congress’s exercise of enumerated powers generally.455 Second, the discretion that Congress may exercise under the Offenses Clause with respect to choice of punishment is supplemented by its discretion under the Necessary and Proper Clause.456 In Bond v. United States, Justice Scalia argued that the Necessary and Proper Clause, coupled with the Article II treaty power, gives Congress only the power to help the President make treaties and not the power to implement them.457 But even if he were correct, using the Necessary and Proper Clause in conjunction with the Offenses Clause is not subject to the same objection because the Offenses Clause is an Article I power to implement treaties.

In practice, Congress is most likely to exercise discretion in determining the means of punishment. For example, with respect to the treaty rights of aliens with which Congress was concerned in the late nineteenth century, Congress could have enacted legislation establishing incentives to encourage greater state enforcement, adopted specific legislation creating a federal crime, or federalized offenses against aliens according to the terms provided under state law (which is what the proposed legislation would have done).458

The Supreme Court’s military commission cases offer further support for the proposition that the Offenses Clause allows Congress discretion with respect to the means of punishment adopted under the Offenses Clause. In Quirin and Yamashita, the Supreme Court not only upheld the United States’s authority to prosecute conduct that was recognized as a war crime under international law, but also upheld Congress’s authority to establish military commissions. In enacting legislation authorizing military commissions, the Court reasoned, Congress had

exercised its authority to define and punish offenses against the law of nations by sanctioning, within constitutional limitations, the jurisdiction of military commissions to try persons for offenses which, according to the rules and precepts of the law of nations, and more particularly the law of war, are cognizable by such tribunals.459

Prosecution of war crimes is obligatory under the modern law of armed conflict, as Congress recognized in adopting the 1996 War Crimes Act.460 However, prosecution of war crimes via military commission is not. Indeed, some states today have eliminated a separate system of military justice altogether, including for their own armed forces. Certainly, nothing under international law requires the establishment of military commissions to prosecute war crimes. Nevertheless, the Supreme Court upheld the establishment of military commissions as a proper exercise of Congress’s authority under the Offenses Clause. This decision suggests that the Offenses Clause not only provides constitutional authority for Congress to impose penalties for “any new international obligation the United States might accept,”461 but also allows Congress some discretion to decide how best to punish conduct that international law prohibits or to meet the United States’s international law commitments.

Finally, it is important to bear in mind that Congress’s authority under the Offenses Clause may be subject to constitutional limits external to that clause.462 A brief discussion of al Bahlul v. United States463 illustrates the point. The defendant, a personal assistant to Osama bin Laden, was convicted by a military commission of conspiracy to commit war crimes, providing material support for terrorism, and solicitation of others to commit war crimes under the 2006 Military Commissions Act.464 On appeal, the D.C. Circuit sitting en banc vacated al Bahlul’s material support and solicitation convictions under the Ex Post Facto Clause, while rejecting the ex post facto challenge to his conspiracy conviction under a “plain error” standard of review.465 The court remanded the remaining issues to the three-judge panel, including whether Congress violated Article III by vesting military commissions with jurisdiction to try crimes that are not offenses under the international law of war.466

Prospectively, Congress clearly has ample Article I authority to establish conspiracy, solicitation, and material support for terrorism as crimes that may be prosecuted in Article III courts. Indeed, to the extent that counterterrorism treaties to which the United States is a party address such conduct,467 our reading of the Offenses Clause bolsters such authority. But as al Bahlul makes clear, Congress’s exercise of its Article I authority can be subject to the limitations of the Ex Post Facto Clause.468

On remand in al Bahlul, the three-judge panel is considering another potential limitation external to the Offenses Clause: whether Article III limits the jurisdiction of military commissions to crimes that are offenses under the international law of war.469 Ex parte Quirin recognized an exception to the Article III right to jury trial, but that exception applies only to “offenses committed by enemy belligerents against the law of war.”470 Not all violations of the law of nations are violations of the law of war.471 If Quirin’s exception is limited to offenses against the international law of war,472 then Article III would prohibit the trial of conspiracy, solicitation, and material support for terrorism by military commissions, notwithstanding Congress’s authority under the Offenses Clause (and its other Article I powers) to criminalize those offenses.473 The Offenses Clause would not permit Congress to avoid this limitation by relabeling a violation of the law of nations (treaty or customary international law) as a violation of the law of war any more than it permitted Congress to relabel murder as piracy back in the nineteenth century.474

In sum, Congress has some discretion under the Offenses Clause to define offenses under customary international law and treaties, but it may not create or relabel offenses that are not recognized by international law. Congress also has discretion in selecting punishment for such offences to choose a means rationally related to what is required or authorized by international law. But of course, Congress’s discretion is subject to whatever other limitations international law and the U.S. Constitution might impose.

Conclusion

The history of the Offenses Clause establishes that the Clause was adopted to allow the United States to enforce all forms of international law, both customary international law and treaties. Although the historic understanding of the “law of nations” as including the “conventional law of nations” has been largely lost in the legal academy, Congress and the Supreme Court have shared this understanding and have consistently applied the Offenses Clause to enforce treaty commitments.

Reading the Offenses Clause to allow enforcement of treaties does not dramatically alter the overall scope of congressional authority. Throughout U.S. history, Congress has been understood to enjoy general power to implement treaties under the Article II treaty power together with the Necessary and Proper Clause. Congress’s other enumerated authorities in the realm of foreign relations, including under the Commerce Clause, have become more capacious over time. Reliance on the Offenses Clause also presumably would not eliminate the federalism concerns relating to criminal statutes articulated by the Supreme Court in Bond.The clear statement rule that the Court applied there to statutes implementing treaties had previously been applied to criminal statutes adopted under Congress’s enumerated Article I powers. Understanding the Offenses Clause to incorporate enforcement of treaties, however, is significant in at least three respects.

First, it recaptures the original understanding of the phrase “law of nations” as used in the Offenses Clause, an understanding that has been obscured by the intensive scholarly attention given to the Alien Tort Statute and the assumption that the phrase must have the same meaning in both contexts. Understanding the Offenses Clause to reach treaties allows us to see the central importance that the Framers placed on complying comprehensively with all of the United States’s international legal commitments—so much so that they established an explicit enumerated authority to define and punish international law violations in addition to Congress’s general constitutional authority to implement treaties under the treaty power and the Necessary and Proper Clause.

Second, reading the Offenses Clause to cover treaties avoids the need to disentangle customary international law from treaty obligations in establishing the constitutional basis for penal legislation intended to enforce international law. From the beginning of the Republic, treaty obligations concerning piracy, safe-conduct, and neutrality were intertwined with customary international law, and the same is true today on a number of other topics, from diplomatic immunity to war crimes. Reading the Offenses Clause to apply regardless of the kind of international law at issue avoids meaningless line drawing and is most consistent with the purpose of the Clause: to provide the national government with comprehensive authority to comply with the United States’s international commitments.

Finally, the Offenses Clause creates a clear Article I basis for congressional power to enforce a range of international treaties in contexts where such authority may otherwise be contested. For example, it establishes a clear additional constitutional basis for the Chemical Weapons Convention Implementation Act that responds to the objections of Justice Scalia in Bond because it does not rest on the Article II treaty power. It likewise establishes a constitutional basis for the Maritime Drug Law Enforcement Act in cases like Bellaizac-Hurtado, where the narcotics trafficking is wholly extraterritorial and may therefore lie beyond the scope of even the Foreign Commerce Clause.

Debates about the implementation of treaties in the U.S. legal system, the limits of Congress’s authority, and the requirements of federalism are bound to continue. But those debates will be more productive if they are informed by a clearer understanding of Congress’s complete power to enforce treaties, including its powers under the Offenses Clause.