Final answer:
McCarthyism in the 1950s is associated with anti-Communist hysteria led by Senator Joseph McCarthy, who made baseless accusations of Communist infiltration in the U.S. government.
Step-by-step explanation:
McCarthyism in the 1950s is most actively associated with a widespread anti-Communist movement in the United States, characterized by unsubstantiated allegations and the practice of making accusations of subversion or treason without proper regard for evidence. This term comes from Senator Joseph McCarthy of Wisconsin who, during this period, repeatedly made claims that Communists and Soviet spies had infiltrated the United States government, notably the State Department.
McCarthy's accusations began to capture national attention after his speech in Wheeling, West Virginia, in 1950. He wielded the fear of communism as a political tool, creating a frenzy by suggesting there was a sizable Communist presence manipulating the federal government from within. Even though he lacked evidence, his influence was substantial, leading to the opening of numerous investigations and the creation of blacklists that wrongly ended or hampered the careers of many in Hollywood and beyond.
Finally, the reach of McCarthyism wasn't just limited to the government or Hollywood. It had a broader societal impact where fear of association with anything remotely considered socialist or Communist stifled free speech and progressive ideas such as state-sponsored health insurance, which failed to take off in the US as it did in Europe owing to the fear of being labeled as supporting 'socialist' ideas.