The main issues of the United States foreign policy during the 1945–1953 presidency of Harry S. Truman include:
- Final stages of World War II included the challenge of defeating Japan with minimal American casualties. Truman asked Moscow to invade from the north, and decided to drop two atomic bombs.
- Post-war Reconstruction: Following the end of World War II, Truman faced the task of rebuilding Europe and Japan. He implemented the Marshall Plan to provide economic aid to Europe and Washington supervised the reconstruction of Japan.
- Formation of the United Nations: Truman played a key role in the formation of the United Nations, which was established in 1945 to promote international cooperation and prevent another world war. Because of the Soviet veto, it was ineffective in most major disputes.
- Cold War: Truman led the nation into the Cold War in 1947, a period of heightened tensions and rivalry between the United States and the Soviet Union. Truman helped form the NATO military alliance. He implemented the policy of containment, which aimed to stop the spread of communism and limit Soviet influence around the world.
- Korean War: In 1950, North Korea invaded South Korea, leading to a bloody conflict that lasted until 1953. Truman authorized U.S. military intervention in the conflict, which led to a protracted and costly war. He rejected the advice of General Douglas MacArthur, and fired him in 1951.
- Nuclear arms race: Truman made the decision to build the hydrogen bomb. He oversaw the development of the U.S. nuclear arsenal and the start of the nuclear arms race with the Soviet Union, which had far-reaching implications for U.S. foreign policy.
Taking office in April 1945 in the last stages of winning World War II, Truman worked with the main American Allies, especially Britain, the Soviet Union and China. He distrusted the Soviets. The challenges were to achieve victory over Germany and Japan; deal with the chaos in Europe and Asia in the aftermath of World War II; handle the beginning of the Cold War with the USSR; and launch new international organizations such as the United Nations and the World Bank. Truman's presidency was a turning point in foreign affairs, as the United States engaged in a liberal internationalist foreign policy and renounced isolationism by engaging in a long global conflict with the Soviet Union and its allies, forming NATO, and fighting China in the Korean War to a deadlock.