Why did anticommunism become a major domestic as well as foreign policy concern during the late 1940s and early 1950s?

In the late 1940s and early 1950s, American fears of internal communists. The people were afraid of what was going to happenin the future and were deployed by anti-Communists in the decade after World War II had a trial run in the late 1930s. There was domestic support for his Cold War foreign policy.