Different fears, same alliance: Multilateralism, assurance and the origins of the 1951 United States–New Zealand–Australia alliance

How do power, interests and threats influence the creation of military alliances? Under what conditions do multilateral and bilateral alliances emerge? Are shared threat perceptions necessary for alliance creation? This article addresses these longstanding questions through developing and refining theories of alliance creation and design and tests them using new archival data from Australia and the United States. The theory and empirics refine balance of threat theory through developing and/or testing other theories regarding the balance of power, threat perception, assurance, signalling and control. Empirically, the article shows that although after the 1950 Korean War the United States wanted Japan to be capable of withstanding Soviet and Chinese challenges, Australia, New Zealand and the Philippines feared that this would allow future Japanese naval militarism. Truman sought to secure regional buy-in to his Japanese settlement through one multilateral alliance, given bilateralism’s costs of assuring multiple allies, but had to settle for several bilateral alliances given regional refusal to ally with Japan. The findings show that bilateral alliances incur previously neglected ‘assurance costs’ and that alliances are possible between states with divergent threat perceptions.