Lawful Ends to Unlawful Wars: Coercion and Voidness in Peacemaking

abstract. Recent calls for a negotiated settlement to Russia’s war on Ukraine neglect whether such a settlement would be lawful. Yet under a settled principle of international law, a coerced treaty is void. This principle, a corollary of the U.N. Charter’s bedrock prohibition on the unlawful use of force, was developed precisely to rule out treaties making concessions to an aggressor in exchange for peace. This Note examines the neglected prohibition on coerced treaties, argues that various proposals for peace in Ukraine are actually unlawful, and concludes by suggesting how the war could lawfully end.

author. I am deeply grateful to Professor Oona Hathaway for her supervision, dialogue, and encouragement throughout this Note’s development. Thomas Poston, Tilly Brooks, Zachary Brown, and Gabriel Klapholz provided valuable comments and support when this work was still in its earliest stages. I also thank the editors of the Yale Law Journal, especially Jan-Phillip Graf, Jeremy Thomas, Nellie Conover-Crockett, Matt Beattie-Callahan, and Ako Ndefo-Haven, for thoughtful feedback and diligent work during the publication process. Most of all, I thank my wife, whose gifts and devotion for the field of international law set the standard to which I aspire here.

Introduction

Russia’s invasion of Ukraine has left more than a million dead or wounded.1 But after almost four years of war, neither side appears close to a decisive victory. All major parties seem to agree that the conflict must end in some sort of negotiated settlement, though they dispute the possible peace terms bitterly.2 Few, however, have raised the question of whether a negotiated peace could even be lawful. That is a perilous oversight.

Under Article 52 of the Vienna Convention on the Law of Treaties (VCLT), “[a] treaty is void if its conclusion has been procured by the threat or use of force in violation of the principles of international law embodied in the Charter of the United Nations.”3 Any peace treaty by which Russia won concessions from Ukraine would fall under the shadow of coercion and, thus, voidness. The prohibition on coerced agreements is derived from the broader prohibition on the threat or use of force between states, which is the foundational principle of the international order established after the World Wars.4 The question of peace between Ukraine and Russia, therefore, reveals a tension that goes to the heart of international law—the pull in one direction toward making peace today and the pull in the other toward holding fast to rules aiming to preserve peace tomorrow.

This tension is a growing pain for a relatively young legal system. Until 1945, war was generally treated as a legitimate tool for states to pursue their interests.5 In that world, binding treaties concluded under the threat of force were unexceptional, even a necessity: how else would victors secure their gains on the battlefield and victims cut their losses? That logic changed after the two World Wars, when the international community, in establishing the United Nations, outlawed the use of interstate force except under the most exceptional circumstances. Under the new norm of international law now codified as Article 52 of the Vienna Convention on the Law of Treaties, a treaty procured by the threat or use of unlawful force would be as invalid as the threat or use of unlawful force itself, and therefore void ab initio (void at conclusion).6 By making coerced treaties void rather than merely voidable, the prohibition was designed not only to protect the consent of coerced parties but also to avert interstate conflict by reducing the incentive for states to wage war on each other.7

But the prohibition on coerced peace agreements complicates cases where the prohibition on war fails. A peace treaty is, by definition, concluded in the shadow of conflict, and the failure to conclude a peace treaty means that hostilities will continue, at least formally. But if the threat of force hangs over all peace treaties, then it might seem that any peace treaty is at risk of voidness by reason of coercion. A conceptual tension emerges: if the concessional peace agreements common in premodern international law may today be invalidated as coercive, then ending an unlawful war without abandoning the legal frameworks that secure peace in general is not so simple.

This Note considers how international law’s prohibition on coerced agreements rightly applies to peace treaties—both in the abstract and in the case of the ongoing Russo-Ukrainian War. In Part I, the Note articulates and analyzes Article 52’s prohibition on coerced treaties, marshaling the prohibition’s history, text, and structure to argue that the Article invalidates treaties that transfer territory from a victim state to an aggressor. Part I also emphasizes that Article 52 is central to upholding modern international law’s foundational prohibition on the threat or use of force between states. To that end, Part II makes an empirical study of post-1945 peace treaties, showing that they overwhelmingly conform to the Article 52 prohibition and contending that robust enforcement of that prohibition is critical to the fragile international stability that has largely prevailed since the World Wars. Part III addresses the concern that the prohibition in Article 52 makes peace more difficult or even impossible once war has broken out, arguing that the prohibition should be upheld in spite of that fear. In Part IV, the Note assesses the possibilities for a negotiated peace in the Russo-Ukrainian War, concluding that while several major proposals for concessional peace agreements now in circulation violate international law, plans under which a lasting ceasefire or Security Council approval preceded a peace agreement are more likely to be lawful. Finally, Part V discusses how these legal conclusions might affect the implementation and enforcement of a voidness finding, arguing that states should take coordinated action to reject any coerced treaty.