Despite striking similarities in their post-World War II security environments, Western Europe and Northeast Asia have since developed distinct types of regional security institutions. In Western Europe, an intricate set of multilateral institutions has arisen as the preferred form of interstate cooperation, whereas the governments of Northeast Asia have largely refrained from region-wide institution building. Instead, they have entered into a series of bilateral alliances with the United States. What explains such disparate patterns of institutional development to preserve peace in the two regions? While extant scholarship emphasizes various economic and cultural factors, I argue that balance-of-power logic consistently drove America’s and its allies’ strategic needs, preferences, and institutional choices. Washington sought to create centers of power in the two regions prosperous and powerful enough to balance against burgeoning Communist threats. The United States pursued a multilateral order in Western Europe because balancing was only possible through the pooling of economic and military capabilities of its allies. Conversely, a bilateral order prevailed in Northeast Asia because its Asian partners did not possess sufficient wherewithal to defend against Soviet and Chinese offensives either individually or collectively. The case studies closely analyze the North Atlantic Treaty of 1949 and the Treaty of Paris of 1951 on the European side and the San Francisco Peace of Treaty of 1951 and the U.S.-Japan Mutual Security Treaty of 1951 on the Asian side, the four agreements that built the institutional foundations for the two regions. By drawing extensively upon unclassified archival records, I trace the negotiation processes between American policymakers and their European and Asian counterparts, as well as their respective internal discussions leading up to the signing of these treaties.