The policy of containment - more specifically the Domino Effect theory - led US policymakers to support intervention in Korea and Vietnam. During the early stages of the Cold War, containment meant preventing the spread of the Soviet Union; however, it quickly evolved to the Domino Theory where containment was to be applied to all forms of communism. This theory posited that if one country were to adopt communism, countries nearby would do the same, which is why the US wanted to prevent the adoption and spread of communism in East and Southeast Asia.
