abstract. At what point does a state’s protection of its interests cross the line? This is the question raised by the protective principle in international law, which permits a state to apply its laws to the conduct of noncitizens—beyond its borders—when such conduct threatens the security or essential interests of the state. Envisioned as a narrow carve-out for governments to regulate grave crimes like espionage and terrorism, the protective principle in recent years has facilitated essentially unbounded jurisdiction “creep.” That is, governments have used it to justify the extraterritorial regulation of a broad and growing range of conduct, from drug trafficking to political speech—with steep costs for state sovereignty and individual liberty. To rectify this problem, this Note proposes a reformulation of the protective principle under a two-prong jurisdictional test. This novel prescriptive solution also carries broader implications for the role of self-protection in international law.

author. J.D. expected 2025, Yale Law School; A.B. 2020, Harvard College. I am sincerely grateful to Professor Oona Hathaway for her mentorship and guidance throughout the writing of this piece. I also thank Professors Harold Koh, Pierre-Hugues Verdier, Paul Gewirtz, and Lea Brilmayer for helpful discussions and suggestions. The YLJ Notes and Comments team provided instrumental feedback. Finally, I am grateful to my parents, Jon and Linda, for their endless support and encouragement.

Introduction

On July 31, 2020, Samuel Chu woke up in his sunny Los Angeles apartment to news that he had been named an international fugitive.1 According to his arrest warrant, he had violated the 2020 Hong Kong National Security Law, though Chu, who is a U.S. citizen, was not sure how.2 He had not been to Hong Kong since 2019—months before the law came into force.3 Yet under Article 38, the law applies “extraterritorially”: it reaches Chu from Hong Kong all the way home.4 This means, of course, that anyone can violate the law from anywhere on earth.

The Chinese government defends the law’s extraterritorial reach under the protective principle in international law. According to this theory of jurisdiction,5 a state can enact laws that regulate the conduct of noncitizens—beyond its territory—when they commit acts against the “security”6 or “essential interests”7 of the state. A basis of jurisdiction tracing back to the Italian city-states,8 the protective principle is playing an important role in Beijing’s effort to, in its words, “take up legal weapons” and build an extraterritorial system of law.9

Though novel in the Chinese context,10 this development is just the latest example of an old problem: the “jurisdiction creep” of criminal law under the protective principle. From 1800s France to post-9/11 America, nations across the globe have enacted statutes that criminalize an increasing breadth of offenses overseas.11 Because the only limiting principle of protective jurisdiction is a state’s essential interests, the more broadly a state defines these interests, the more widely its laws will reach. The conceptual expansion of security in the twenty-first century has further facilitated this trend.12

Without limits, the reach of criminal law across borders comes with costs for the interests of both states and individuals, as the Permanent Court of International Justice (PCIJ) first noted in the landmark Lotus case.13 When the court handed down this decision in 1927, it affirmed that jurisdiction to enact statutes represents a core right of state sovereignty: the right of a nation to build a rule of law, within its borders, to the “exclusion” of other states.14 This interest is undermined when a government reaches its statutes into the territory of other nations, especially when these statutes conflict—and they often do—with the other states’ senses of justice. Laws that apply everywhere also subject individuals to criminal penalties of which they have no knowledge and to the authority of governments with which they have no ties.15

Even more fundamentally, the impulse to criminalize conduct thousands of miles from home threatens to tear at the fabric of “[w]orld [s]ociety.”16 That is, in a pluralistic legal order where states maintain bitter disagreements about how to govern and which laws to pass, coexistence depends on the observance of some legal boundaries.17 Recent bilateral disputes over the scope of extraterritoriality under the protective principle illustrate its destabilizing effects on international relations.18

Scholars have taken notice of this issue and considered solutions.19 Noting that the protective principle is uniquely susceptible to jurisdiction creep, they have proposed new formulations of it. The two primary reformulations in the literature are vulnerable to their own objections, however. The first, springing from an early-twentieth-century effort to codify a treaty on jurisdiction, does not account for states’ modern uses of the protective principle.20 The second proposes a framework—rooted in self-defense—that is arguably as manipulable as the current one.21 Moreover, neither grapples with the sophisticated strategies of some states, including China, to integrate the protective principle throughout their legal systems.22

After providing an original analysis of the protective principle, this Note proposes a better way. Specifically, it offers a novel formula to limit states’ exercises of protective jurisdiction so that they regulate extraterritorial conduct only when they have a “legitimate interest[]” in self-protection at stake.23 This change ensures more targeted applications of the protective principle to avoid infringing on states’ interests and subjecting individuals to infinite layers of criminal prohibitions.

This formula takes the form of a two-part test. The first part adapts principles developed in the context of international trade law to identify criteria that can suggest whether there is a “sufficient nexus between” the conduct a state seeks to regulate and its essential interests.24 This part relies on an examination of (1) analogous laws in state practice and (2) the “content” and “structure” of an extraterritorial regulation.25 The second part of the test considers whether there is a nexus between the state and the perpetrator of the act to justify the state’s exercise of jurisdiction. It assesses whether the state and the actor have substantial ties—a thick and continuing relationship—that would form an equally necessary connection between the state and the foreign controversy.26

As I will explain below, this test is anchored both in the insights of the Lotus case—the foundational judgment on extraterritorial jurisdiction—and in the genuine-connection doctrine of customary international law.27 Admittedly, as there is no treaty or specialized court that regulates states’ exercises of jurisdiction, governments would apply the test in a decentralized fashion.28 Nonetheless, adopting this framework could have immediate effects on states’ ability to obtain custody of non-nationals through extradition. Over time it could also become integrated with more formal structures of international law.

This Note proceeds in four Parts. Part I begins with background on the theoretical grounding of the protective principle. It argues that, though “protection of the state” provides a justification for the existence of the protective principle, it is insufficient as a limiting framework. Consequently, the principle allows for essentially unbounded exercises of extraterritoriality. Part II tracks the effects of protective-jurisdiction creep on state sovereignty, individuals’ interests, and international relations. I use the Chinese legal system as my main case study because China’s widescale use of the protective principle provides the best window into understanding the principle’s implications today. The pace with which Beijing has embraced the principle also brings urgency to the development of new jurisdictional limits. Part III then proposes a two-part test to limit states’ exercises of protective jurisdiction and applies the test to canonical and emerging instances of extraterritoriality. Finally, Part IV discusses the implications of this framework for broader issues in international law.

As I note in Part IV, the implications of this framework extend beyond the protective principle. They get at central questions in international law: what a state can do—and how far it can go—to protect its interests, and how its interests interact with those of all other states. Deriving broader principles from this study of protective jurisdiction, this Part argues that now more than ever, our answers to these questions must grapple with the fact that as nations have faced challenges of an increasingly global nature, their interests have become more intertwined—and their “self-protection” has, too. This calls for a reconceptualization of the role of unilateral protective measures in international law.