What conditions lead to McCarthyism during the Cold War?

The idea that it was necessary to guard against people seeking to overthrow the U.S. government took root early in the 20th century. Advances made by the Soviet Union following World War II, coupled with the victory in 1949 of the Chinese Communist Party in establishing the People's Republic of China and the apparent inability of the United States to prevent the spread of communism, were among the factors causing fear of communist infiltration in the United States.

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