This thesis analyses an international crisis in the mid-1960s known as the Malaysian-Indonesian Confrontation (Konfrontasi). It began in January 1963 and effectively ended with the establishment of military rule in Jakarta during late 1965. The focus of the thesis is to examine how the four western powers most involved in the crisis - Britain, the United States, Australia and New Zealand - responded to Confrontation and, as a consequence, how they intended to protect their respective strategic interests in Southeast Asia. In particular, the thesis seeks to place both the crisis, and the reactions of these allies, within the regional and international context of the period under review. Accordingly, issues such as Britain's continued military presence east of Suez, the escalation by the US of the war in Vietnam, the West's containment of an increasingly assertive communist China and the role of the Australasian dominions in British and American policies regarding Southeast Asia, are all examined in detail. Finally, the thesis is developed chronologically. It begins in 1961 when Britain finalised its plans for decolonisation in the region by establishing a greater Malaysia federation. It ends with the 'coup' in Jakarta and the latter months of 1965, when the Wilson government commenced preparations for a British withdrawal east of Suez. Extensive research was carried out in the archives of the four western powers. In Britain this mostly consisted of viewing recently declassified documents at the PRO. In the United States materials were gathered from the JFK and LBJ presidential libraries, the US national archives and the State Department's Foreign Relations of the United States series. In Australasia, research was primarily conducted at Australian Archives, Canberra and the Ministry of Foreign Affairs and Trade, Wellington.