In the 1940s and 1950s, Americans were primarily afraid of two significant threats: communist takeover and nuclear warfare. The post-World War II atmosphere was heavily influenced by the emergence of the Soviet Union as a superpower and the spread of communist ideology worldwide. The successful testing of the atomic bomb by the Soviet Union in 1949 heightened fears of nuclear conflict, especially as the U.S. and the USSR became embroiled in a Cold War characterized by espionage, propaganda, and military build-ups.
The conviction of high-profile individuals, such as Alger Hiss, for espionage further fueled suspicions that communists had infiltrated various levels of American society, including the government. This paranoia was seized upon by figures like Senator Joseph McCarthy, who claimed to be combating the communist threat and became a central figure in the witch hunt against alleged communists.
While fears of a resurgence of fascism, such as a Nazi party revival, could have lingered from World War II, the immediate fear during this period was more directed toward communism and the potential for nuclear conflict. Thus, the overarching fears during the 1940s and 1950s were primarily centered around the dual threats of a communist takeover and the reality of nuclear warfare, making the environment ripe for hysteria and the acceptance of extreme measures, such as those initiated by McCarthy.