The Truman Doctrine was a foreign policy created by President Harry Truman that stated that the US would offer political, military, and economic support to any democratic countries that were under threat from authoritarian forces. On March 12, 1947 Truman unveiled the Truman Doctrine in an address to the US Congress. In this address he stated "It must be the policy of the United States to support free peoples who are resisting attempted subjugation by armed minorities or by outside pressure." When South Vietnam found itself being threatened by communism, this policy was used to justify US involvement in Vietnam. As a result, american troops were sent to Vietnam to help defend South Vietnam against the outside forces of communism, and the US found itself involved in the Vietnam War.
April 7, 1954, President Dwight D. Eisenhower gave a speech to warn the U.S. of the threat of communism in Vietnam. The plan was that the U.S. would stop communist aggression in Southeast Asia. This strategy was associated with The Domino Theory. Eisenhower likened Vietnam to a domino. The falling of the domino symbolized Vietnam falling to communism. If Vietnam became a communist nation then other countries such as Laos, Cambodia, Thailand, Burma, Malaysia and even Indonesia would also be forced to accept communism. The Domino Theory persuaded Americans to join the Vietnam War. America did not want communism, especially since it brought about corruption to Germany, Russia and Poland during WWII. The only alternative was to wage war in Vietnam.