On March 12, 1947, President Harry S. Truman declared the Truman Doctrine before US Congress. Truman asked Congress to provide economic, political, and military assistance to democratic nations under threat of authoritative and communist forces in an effort to secure international peace and US national security. In short, Truman asked Congress to take an active role in the fight against the spread of communism and to support foreign democratic nations.

Truman spoke to Congress on the need for the United States to intervene against major threats to democracy in the aftermath of World War II. In particular, Truman asked Congress to pledge $400 million in the form of civilian and military personnel and aid to support the Greek and Turkish governments against communism. At the time, the US government believed that the Soviet Union was supporting the Greek communists in the Greek Civil War in an effort to ultimately reshape Greek policy with communist beliefs.

Truman argued that a communist victory in the Greek Civil War would endanger the political stability of Turkey and the Middle East. For the first time in American politics, Truman asked the United States to take an active effort in assisting foreign democratic nations if such actions were in the best interest of the United States.

The Truman Doctrine set the foundation for modern US foreign policy as a leader in the free world, democracy, and the fight against communism. Many influential individuals such as George Marshall, Dean Acheson, and others also promoted this new foreign policy in an effort to contain the spread of communism and promote the spread of democracy.

The Truman Doctrine reshaped U.S. foreign policy in a major way. Under the Truman Doctrine, the United States abandoned its isolationist attitude and began to take active role in the internal affairs of foreign countries – which is still the general policy of the US today.

To sum it up in Truman's words, the Truman Doctrine has become "the policy of the United States to support free peoples who are resisting attempted subjugation by armed minorities or by outside pressures."