The Truman Doctrine was a pivotal U.S. foreign policy established in 1947, aimed at containing the spread of communism during the early years of the Cold War. It was articulated by President Harry S. Truman, who pledged support to countries resisting communist influence, particularly in Greece and Turkey. This doctrine marked a significant shift in American foreign policy, moving from isolationism to a more interventionist approach. By providing military and economic aid, the U.S. sought to prevent the expansion of the Soviet Union's influence, thereby shaping international relations for decades to come.