The United States followed a policy of containment during the Cold War in response to the spread of communism. The policy of containment began in the late 1940s to stop the spread of communism in Europe and Asia. It became U.S. policy for decades.
Following World War II, most of the Eastern Europe countries had communist governments and were under Soviet control. In 1949, the Chinese Revolution established a communist government in China.
In Europe, the Marshall Plan and the North Atlantic Treaty Organization (NATO) were efforts to contain communism. The Marshall Plan was a program that provided $13 billion in U.S. aid to help rebuild Western European economies after the end of World War II. By creating strong economies and stable democracies in Western Europe, the U.S. was assured of allies against the Soviet Union. NATO was created in 1949 by the United States, Canada, and Western European countries to provide collective security against the Soviet Union.
In Asia, the policy of containment was the basis for U.S. involvement in the Korean and Vietnam wars. The Korean War started as a civil war between North and South Korea. The war quickly became international when the United Nations (led by the U.S.) joined to support South Korea and communist China entered on the side of North Korea. In Vietnam, North Vietnam wanted to unify the entire country under a single communist government. The government of South Vietnam, however, was more closely allied with the U.S. The U.S. sent military advisers and combat units to support South Vietnam. The Soviet Union and China sent weapons, supplies, and advisers to support North Vietnam.