The Gulag was a vast network of "slave labor" camps run by the Soviet Union from the 1920s to the 1950s. Ever since the Soviet Union was founded in 1917, it imprisoned people who spoke out against it or were otherwise dangerous. Imperial Russia in previous decades had a similar system of prison camps. But the Soviet Union camp system grew to be one of the largest prison systems in existence. The Soviet camp-system was set up under Vladimir Lenin.