This Article challenges the conventional wisdom that states are always free to choose whether to participate in multilateral regimes. We argue that contemporary international law requires multilateralism in at least five domains: (1) disputes involving rivalrous claims to territorial jurisdiction, (2) disputes involving conflicting legal entitlements, (3) the administration of common resources, (4) threats to international peace and security, and (5) grave breaches of international human rights and international criminal law.
International law’s commitment to mandatory multilateralism, we claim, is explained by its organizing principles of sovereign equality and joint stewardship. Sovereign equality provides for states’ mutual independence within an international legal order structured in part by a prohibition on unilateralism. Similarly, when international law assigns collective responsibility to states to regulate certain global public goods (e.g., the deep ocean floor, international peace and security), joint stewardship dictates that states must regulate those goods multilaterally rather than unilaterally.
Where mandatory multilateralism applies, it imposes a substantive requirement that states pursue equitable solutions to controversies by balancing their own legal interests with the interests of others. 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. If states are unable to agree on a negotiated solution or a forum for arbitration, they must maintain a dialogue and refrain from taking steps that would prejudice negotiations.
The final section of the Article explains how mandatory multilateralism offers lessons with respect to three current controversies: 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.
