Did the Truman Doctrine stop the spread of communism in Vietnam? Why or why not?

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.

The Truman Doctrine was an American foreign policy whose stated purpose was to counter Soviet geopolitical expansion during the Cold War. It was announced to Congress by President Harry S. Truman on March 12, 1947, and further developed on July 12, 1948, when he pledged to contain threats in Greece and Turkey.

The Truman Doctrine, 1947. With the Truman Doctrine, President Harry S. Truman established that the United States would provide political, military and economic assistance to all democratic nations under threat from external or internal authoritarian forces.

President Truman took actions to try to stop the spread of communism. As communism spread through Eastern Europe, we developed a policy called Containment ... The European Recovery Program offered aid to countries fighting the spread of communism. Greece and Turkey were two countries that benefited from this aid.

The Truman Doctrine was an American foreign policy whose stated purpose was to counter Soviet geopolitical expansion during the Cold War. It was announced to Congress by President Harry S. Truman on March 12, 1947,[1]:547-9 and further developed on July 12, 1948, when he pledged to contain threats in Greece and Turkey. Direct American military force was usually not involved, but Congress appropriated financial aid to support the economies and militaries of Greece and Turkey. 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. Historians often use Truman's speech to date the start of the Cold War.