Since the Russian Revolution in 1917, the conflict between communism and anticommunism has played a significant role in shaping American society and culture. The Red Scare of 1919–1920 was partly due to American fears of communist subversion. Until 1933 the United States refused to have diplomatic ties with the Soviet Union. In the 1930s some Americans viewed the Soviet Union as a potential ally against Nazi Germany. These views changed with the signing of the Hitler-Stalin nonaggression pact in August, 1939 that opened the way for Germany's attack on Poland and the division of that country between the Nazis and Soviet Union.

In the wake of the Hitler-Stalin pact critics argued that Communism and Nazism were not at opposite poles of a straight-line ideological continuum. Rather, Communism and Nazism had to be understood as the totalitarian ends of a horseshoe that bent toward each other. Democratic societies were...