During World War I, the Justice Department led covert operations to detect, silence, and sometimes arrest suspected German sympathizers. Congress passed the Espionage Act of 1917 and the Sedition Act of 1918, calling for investigations of war critics and allowing convictions of disloyal behavior. Attorney General Thomas Gregory stated, “I doubt if any country was ever so thoroughly and intelligently policed in the history of the world.”

Undercover operatives would spy, secretly break into people’s homes, and even harass individuals to find suspected traitors. While no one was immune to these secret investigations, several groups were targeted, including German Americans, African Americans, clergymen, and labor groups.