International law depends not only on treaties and institutions, but on the conduct of powerful states. For much of the 20th century, the United States positioned itself as both architect and guardian of the international legal order that prioritised sovereignty, collective security and rules-based governance. This role was institutionalised through the creation of bodies such as the United Nations, the Bretton Woods institutions, and, later, NATO, which incorporated American power within multilateral frameworks. By promoting norms of non-aggression, dispute resolution and economic interdependence, the US sought to stabilise a post-war world while legitimising its leadership.