Final answer:
The U.S. policy to prevent the spread of communism during the Cold War was known as containment, which involved economic, military, and diplomatic strategies both in Europe and Asia, and internal security measures within the United States.
Step-by-step explanation:
The United States adopted a foreign policy known as containment during the Cold War era. This policy aimed to prevent the spread of communism beyond the countries where it was already established, particularly beyond the Soviet Union and the nations of Eastern Europe.
In Europe, the U.S. implemented the Marshall Plan, providing extensive economic assistance to rebuild and stabilize European countries to resist the allure of communism. Meanwhile, the U.S. formed the North Atlantic Treaty Organization (NATO) as a collective defense system against potential communist expansion. In Asia, containment policies led the United States to involve itself in conflicts like the Korean War and later the Vietnam War, aiming to prevent further spread of communism in these regions.
Within the nation, efforts were also made to root out communist influences through various domestic policies and legislative actions. The policy of containment remained a cornerstone of U.S. foreign policy throughout the duration of the Cold War.