McCarthyism refers to the political phenomenon in the United States during the late 1940s and 1950s, characterized by intense anti-communist sentiment led by Senator Joseph McCarthy. It involved the aggressive investigation and persecution of individuals suspected of communist affiliations, often without substantial evidence. This period is marked by fear, paranoia, and violations of civil liberties, as many faced public accusations, blacklisting, and loss of employment. McCarthyism ultimately contributed to a broader culture of suspicion and distrust in American society.