The UN Charter focuses on states as the central actors in the international system, defining as a multilateral action when three nation-states cooperate in a field of common interest. Today, nation-states are increasingly paralysed into inaction due to political divisions or great power rivalries. Hence, they are failing to effectively utilise collective action. Subnational entities are stepping into this vacuum to deliver on core functions embedded in the UN Charter, redefining effective collaboration on a transnational scale – what we call micro-multilateralism.