The Truman Doctrine was part of the initial response of the U.S. to Soviet aggression in the early years of the Cold War. The Soviets under Premier Joseph Stalin were continuing to expand their influence in Eastern Europe. Stalin said in a 1946 speech that peace was impossible
under the present capitalist development of the world economy.
It was apparent that the Soviets intended world domination. Truman's Secretary of State, James F. Byrnes, threatened the use of nuclear weapons to stop Soviet aggression, but was ignored. Later, when the Soviets worked to undermine the governments of Greece and Turkey, President Truman said in a speech:
I believe that it must be the policy of the United States to support free peoples who are resisting attempted subjugation by armed minorities or by outside pressures.
This remark became known as the Truman Doctrine and also became part of the greater U.S. goal of containing the spread of communism. Truman's position was that if the U.S. did not support the governments of Greece and Turkey, they would collapse and those countries would become part of the Soviet bloc. A portion of this attempt was the Berlin Airlift to prevent the collapse of West Berlin. Containment became an essential element in U.S. actions to stop the spread of communism in Vietnam.