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 during the Russian Revolution, it imprisoned people who spoke out against it or were otherwise dangerous. Imperial Russia in previous decades had a similar system of katorga 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. It reached its peak during Joseph Stalin's rule from the 1930s to the early 1950s.  Many of the prison camps were in Siberia.