Within a decade of its 1945 declaration of independence from Dutch colonial rule, Indonesia emerged at the vanguard of the global Non-Aligned Movement. Leveraging Western Bloc as well as Sino-Soviet interest in the new nation, Indonesia's president, Sukarno, simultaneously secured economic aid and other support from both sides while maintaining a precarious domestic balance of power between the right-wing of the Army and the Indonesian Communist Party (PKI). However, by the early 1960s, as Sukarno began to take a more aggressive anti-imperialist posture toward the West, power began to shift in favor of the PKI and its radical nationalist allies. Indonesia's Cold War "slide toward communism," long a troubling prospect to the United States, thus became a critical and urgent focus of U.S. foreign policy.

Indonesia's second largest city, Surabaya, was one of the strongest bases of support for both Sukarno and the PKI and a hub of overt and covert U.S. anti-communist operations. However, scholars have long overlooked its role as a critical site of the Cold War in Southeast Asia. As U.S.-Indonesian relations deteriorated and street-level anti-Americanism escalated, U.S. officials in Surabaya, forged alliances with local anti-communist collaborators and ramped up operations aimed at overthrowing Sukarno and destroying the PKI. Although it seemed at first that their efforts might not succeed, a failed `PKI coup attempt' on 1 October 1965 provided the justification for both of these objectives to be conclusively achieved. The campaign of mass violence that subsequently took place conclusively changed Indonesia's political direction and paved the way for improved U.S.-Indonesian relations. This dissertation reveals new details about the 1965-66 purge of the Left in Surabaya and about the bilateral relations and political conflict that preceded it. Examining these topics from the lens of microhistory suggests that this method offers an equally valuable way to approach the broader study of U.S. foreign policy, political violence, and the Cold War itself.