Hoover’s career in the Justice Department covered two periods of intense public fear regarding the threat of communism and other left-wing radicalism. The first came after World War I, when the triumph of communism in Russia provoked fears that radicals would exploit ongoing labor disputes in the United States. This culminated in the “Palmer Raids,” the mass arrest and deportation of noncitizens suspected of radical leanings. The second came at the beginning of the Cold War, when the antagonism between the Soviet Union and the United States, coupled with the communist takeover in China, led many to suspect that communists were infiltrating American politics and society. Hoover was a strong supporter of both campaigns, although in the latter Red Scare he disapproved of Senator Joseph McCarthy when his reckless accusations of communist infiltration of the Army proved embarrassing.

The so-called Lavender Scare, an effort to purge the federal government of gay people, arose soon after the end of World War II. America at the time regarded relationships between members of the same sex as perversions, and a 1948 report by sexologist Alfred Kinsey that gay culture was far more widespread than assumed led to a panic. There was also fear that gay people in government could be vulnerable to Soviet espionage efforts, whether as targets of blackmail or because their presumptively inferior moral character could make them susceptible to betraying their country.