Domestically, what events fueled the fear that communism was a real threat in the US

The fear of communism in the United States was a manifestation of political anxiety over the infiltration of international influences, namely tied to Soviet Russia, during the 20th century. The philosophical basis of this fear was based on the significant differences between capitalism and communism as economic systems, while the most noteworthy historical examples of it were the Red Scare after World War I, McCarthyism in the 1950s and the Cold War.