Final answer:
The Truman Doctrine promised that the United States would support nations threatened by Communism, signifying a policy of containment aimed at preventing the spread of Communist influence following World War II.
Step-by-step explanation:
The Truman Doctrine was a significant policy in the era of the Cold War, articulated by President Harry S. Truman in 1947. The key point of the Truman Doctrine was that the United States would support free peoples who were resisting subjugation by armed minorities or by outside pressures, which is to say, resisting Communist forces. In essence, this doctrine meant that the United States would provide assistance to countries threatened by Communism.
The doctrine was catalyzed by events in Greece and Turkey, where Communist parties were gaining influence. Responding to this, the U.S. Congress approved $400 million in aid to help Greece and Turkey combat these communist threats. This interventionist approach signified a departure from previous American isolationist policies, underlining a commitment to the strategy of containment, which sought to prevent the spread of Communism beyond where it had already established during the post-World War II era.