The Truman Doctrine stated that the United States would support "free peoples who are resisting attempted subjugation by armed minorities or by outside pressures."
U.S. President Harry S. Truman made the proclamation in an address to Congress on March 12, 1947 amid the crisis of the Greek civil war (1946-1949). The doctrine was specifically aimed at assisting governments resisting communism. Truman insisted that if Greece and Turkey did not receive the aid that they needed, they would inevitably fall to communism with the result being a domino effect of acceptance of communism throughout the region.
Truman signed the act into law on May 22, 1947 which granted $400 million in military and economic aid to Turkey and Greece.