The efforts of the Bush administration in the early 2000s to establish democratic regimes in Afghanistan and Iraq reflect an American foreign policy tradition that began at the end of World War II. The pairing of national security interests with the success of foreign regimes (and, specifically, regimes headed by charismatic strong men) was a common feature of Cold Warera foreign policy employed by every presidential administration from Harry S. Truman through Ronald Reagan. The U.S. support for President Ngo Dinh Diem of the Republic of Vietnam was a notable failure within this tradition. Americas disillusionment with Diem, and its subsequent complicity in his overthrow and murder, marked the beginning of its direct military involvement in Vietnam. Two-and-a-half million U.S. troops would eventually serve in Vietnam in a failed effort to prevent the Democratic Republic of Vietnam from uniting the country under a communist regime. Examination of the U.S. partnership with Diem during the Eisenhower and Kennedy administrations illuminates factors that led to its demise and may help to prevent their future repetition. This thesis argues that both the Eisenhower and Kennedy administrations focused their aid programs on military security at the expense of political and economic reform, thus failing to address the political inequities that ultimately led to Diems demise. American military aid, calculated to support Diem, ultimately provided the foundation for the military coup that overthrew him. This thesis argues that the Diem experiment shows, first, that military security cannot be a substitute for political stability, and second, that limited-liability commitmentslike the one to Diemmay prove more politically consequential than they first appear, once they start to unravel.