With skepticism about international norms and institutions on the rise around the world, many commentators have argued that multilateralism faces an uncertain future. Major fractures have appeared in international legal order, including Britain’s messy divorce from the European Union and the United States’ controversial decisions to reject the Trans-Pacific Partnership, withdraw from the 2015 Paris Agreement and the U.N. Human Rights Council, and undermine the World Trade Organization (WTO) by sidestepping its dispute-resolution mechanism and blocking appointments to its Appellate Body. While the path forward remains unclear, for now many states are reassessing the strategic value of multilateral cooperation and are recalibrating their international commitments across a wide variety of contexts.

This Article provides a new lens for critically evaluating the current backlash against multilateral norms and institutions. In the past, legal scholars and political scientists have developed sophisticated theories to explain the political dynamics and social norms that inform states’ decisions to participate in, or withhold their participation from, multilateral norms and institutions. This Article, in contrast, poses a different question: when does international law require multilateralism?

Framing the question in this way may strike some readers as counterintuitive. Although international lawyers recognize that international legal norms and institutions are products of multilateral action, some accept a strong version of voluntarism and assume that states are always free to decide for themselves whether they will participate in cooperative international legal regimes or proceed unilaterally. Perhaps in part for this reason, legal scholars have not studied systematically the extent to which international law requires states to cooperate with their peers in developing international norms and institutions. In this Article, we make the case that multilateralism is often mandatory under contemporary international law, and we explain when, why, and how this is so.

We use the term “multilateralism” to denote the coordination of national policies and practices among multiple states in a manner that reflects due regard for the participant states’ respective legal rights and authority to represent their people internationally. Although legal scholars typically distinguish “multilateralism” from “bilateralism,” the crucial distinction for this Article is between actions that states are entitled to take on their own or unilaterally, and actions they are required to take in concert with other states or with due regard to the legitimate interests of the people represented by other states. In other words, the key distinction for present purposes is between unilateral and non-unilateral action, where non-unilateral action is joint activity undertaken by two or more states. We define multilateralism as “mandatory” when states lack discretion under international law to make public policy decisions unilaterally in relation to matters of global concern.

Our argument is that a robust set of legal norms now require and govern international cooperation, these norms apply across a broad range of subject areas, and they impose a common set of substantive and procedural requirements wherever they apply. In several domains, mandatory multilateralism is now the norm. We group these areas into five general categories: (1) territorial disputes, (2) conflicting entitlements, (3) common resources, (4) international peace and security, and (5) international human rights and international criminal law. Whenever a controversy subject to international law falls into one of these categories, the law forbids states from imposing their will unilaterally on their peers.

We consider mandatory multilateralism to be explained by the principles of sovereign equality and joint stewardship as international law’s immanent organizing principles. Sovereign equality provides for states’ mutual independence from each other within an international legal order structured in part by a prohibition on unilateralism. Similarly, when international law assigns collective responsibility and joint authority to states to regulate certain global public goods on behalf of humanity (e.g., the deep ocean floor, endangered species, international peace and security), joint stewardship dictates that states must regulate those goods multilaterally rather than unilaterally. Mandatory multilateralism is thus an institutional expression of the prohibition against unilateralism, and it gives effect to the principles of sovereign equality and joint stewardship.

Where mandatory multilateralism applies, it imposes a variety of substantive and procedural requirements. Substantively, mandatory multilateralism requires states to pursue equitable solutions to international controversies with an eye to balancing their own legal rights and authority, on the one hand, with the legal rights and authority of other individual states and the international community collectively, on the other. Within mandatory multilateralism’s domain, states also bear procedural obligations to investigate and consult with other interested states, negotiate in good faith, and if negotiations stall, submit to third-party dispute resolution. In cases where states are unable to agree on a negotiated solution or a forum for arbitration, they must maintain a continuous dialogue and refrain from taking steps that would prejudice the outcome of negotiations.

Mandatory multilateralism offers important lessons for a wide variety of current international controversies, e.g. the South China Sea dispute, the United States’ pending withdrawal from the 2015 Paris Agreement, and Bolivia’s efforts to compel Chile to negotiate over territorial access to the Pacific. In each of these settings, mandatory multilateralism limits state discretion to go at it alone. First, mandatory multilateralism requires states to resolve territorial disputes in the South China Sea through consultation, negotiation, and third-party dispute resolution, and it strengthens the legal case against China’s militarization and island building within the Sea. Second, although mandatory multilateralism might not require the United States to remain a party to the Paris Agreement, it prohibits the United States from ignoring the global impacts of its climate policies and withdrawing entirely from multilateral engagement. Third, the theory of mandatory multilateralism we develop explains why international law requires coastal states like Chile to cooperate in facilitating landlocked states’ access to the sea, but it does not demand that they entertain negotiations over the possible transfer of their own territory to landlocked states. Taken together, these case studies demonstrate mandatory multilateralism’s far-reaching (but not unlimited) implications for contemporary interstate relations.

Evan Fox-Decent’s and Evan J. Criddle’s article “Mandatory Multilateralism” has been published in the American Journal of International Law 113, no. 2 (2019): pp. 272-325.

Access to the article is available here.