Containment was a United States policy using numerous strategies to prevent the spread of communism abroad. A component of the Cold War, this policy was a response to a series of moves by the Soviet Union to enlarge its communist sphere of influence in Eastern Europe, China, Korea, and Vietnam.
In 1947, President Harry S. Truman pledged that the United States would help any nation resist communism in order to prevent its spread. His policy of containment is known as the Truman Doctrine
First laid out by George F. Kennan in 1947, Containment stated that communism needed to be contained and isolated, or it would spread to neighboring countries. The US's attempt to stop the spread of communism and "Russian expansive tendencies" through economic and military measures.