What was the truman doctrine and what was the cause of its creation

The Truman Doctrine was an American foreign policy whose purpose was to contain Soviet geopolitical expansion during the Cold War.

More generally, the Truman Doctrine implied American support for other nations allegedly 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.