The Truman Doctrine arose from a speech by President Harry Truman, but it has informally become the basis of the U.S. foreign policy during the Cold War and afterwards. Historians often refer to the Truman speech as the day the Cold War started, because the policy was geared towards containing the expansion of the Soviet Union and communism. Previously, the U.S. always had a stance of withdrawing from conflicts that were not directly affecting the U.S., but after Truman's Doctrine was approved, interventions started to happen more frequently in far away countries.
After the Greek Civil War broke out in 1945 against the Greek Communist party, Britain, having supported Greece for years, was close to bankrupt and had to withdraw most of its support. In 1947, Great Britain asked the U.S. to take over this role and Truman made his famous speech during a joint session of Congress in a plea to provide financial ant military assistance. He also asked for support for Turkey, which had similar problems. Truman said that his Doctrine would be a U.S. policy that supports free people that were threatened by armed minorities and outside pressures. At the time, Truman thought that the Soviet Union was actively supporting the Greek communists, which also may have influenced his decision. Congress was controlled by Republicans, who supported this policy and they sent $400 million over to Greece, and managed to end the threat without military intervention. Both countries joined NATO in 1952, in which their protection is guaranteed through a military alliance.
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