Soviet espionage in the United States

As early as the 1920s, the Soviet Union, through its GRU, OGPU, NKVD, and KGB intelligence agencies, used Russian and foreign-born nationals (resident spies), as well as Communists of American origin, to perform espionage activities in the United States, forming various spy rings. Particularly during the 1940s, some of these espionage networks had contact with various U.S. government agencies.