He created the The Truman Doctrine. It was an American foreign policy created to counter Soviet geopolitical expansion during the Cold War. It was first announced to Congress by President Harry S. Truman on March 12, 1947. The Truman Doctrine implied American support for other nations threatened by Soviet communism. The Truman Doctrine became the foundation of American foreign policy, and led, in 1949, to the formation of NATO, a military alliance that is still in effect. Historians often use Truman's speech to date the start of the Cold War.