The Red Scare was a period of anti-communist and anti-radical hysteria that gripped the United States after World War I and the Bolshevik Revolution. In some ways, it was an outgrowth of the anti-radicalism that marked the home front during World War I. During the war, outspoken dissidents and members of the Socialist and Communist Parties and even labor union members were imprisoned for violating the Espionage and Sedition Acts.
After the war, Americans succombed to a reflexive xenophobia, made even worse by the outbreak of the Bolshevik Revolution. Politicians eager to exploit popular fears of communism and other forms of radicalism condemned labor unions and other groups as un-American. The events most associated with the Red Scare were the so-called "Palmer Raids" initiated by U.S. Attorney General A. Mitchell Palmer. Across the country in 1919 and 1920, Palmer's lieutenants, including an up-and-coming young detective named J.Edgar Hoover, launched raids against people suspected of radical activities. They uncovered little evidence of a massive government plot, but dozens were arrested and many people who were not American citizens were deported.
The Red Scare was also the context for the immigration quotas imposed during the early 1920s, which practically banned immigration from Eastern and Southern Europe, considered hotbeds for radicalism.