The idea that the United States is bequeathed the special mission of leading mankind toward liberty has dominated U.S. foreign relations since the American Revolution. It remains the most pervasive theme in Americans' thought about the world to the extent that over time, it has become firmly embedded in the nation's historical and cultural consciousness. A study of diplomatic, intellectual, and cultural history, America in the World: Ideology and U.S. Foreign Policy, 1944-1950 examines the impact of this exceptionalist vision on the policies and public debates that influenced Americans' thinking about their role in the world from the beginning of their efforts to design the global post-World War II order to the outbreak of the Korean War in 1950. Believers in Lockean progress and advocates of modernization, the administrations of Franklin Roosevelt and Harry Truman sought to establish a one-world order based on American liberal political and economic ideals. At the heart of this American-designed postwar world stood the United Nations, created to ensure collective security and foster a spirit of international collaboration, and transnational institutions like the World Bank and the International Monetary Fund, envisioned to protect the global economy and promote free trade. These institutions served as concrete articulations of U.S. national interests yet at the same time they were intended to inaugurate a "New Deal" and a "Fair Deal" for the world. Interpreting American post-war and Cold War policymaking through the lens of exceptionalism provides a complementary methodological framework to the national security or economic theses more commonly employed to describe this period. When the Soviet Union refused to accept the American-designed one-world order, the American response - inside and outside of government - was overwhelmingly shaped by ideology. While economic considerations and national security influenced U.S. Cold War policy, this dissertation demonstrates that it was the challenge posed by Moscow's universalist aspirations and Communism's inherent teleological ideology that caused Americans to turn the Cold War into a battle for a way of life.

This work examines the actions of the Joint Chiefs of Staff during the first year of the Korean War. Officially created in 1947, the Joint Chiefs saw their first true test as an institution during the conflict. At various times, the members of the JCS failed to issue direct orders to their subordinate, resulting in a divide between the wishes of President Truman and General MacArthur over the conduct of the war. By analyzing the interaction between the Joint Chiefs and General Douglas MacArthur, the flaws of both the individual Chiefs as well as the organization as a whole become apparent. The tactical and strategic decisions faced by the JCS are framed within the three main stages of the Korean War.