Prison labor camps, popularized by the author Solzhenitsin in after Stalin died. Solzhenitsin was arrested as an officer in WW2 when military censors caught him sending a letter critical of Stalin. After his stint at a gulag, he wrote an embellished account about his time there,and gulags became one of the atrocities of the USSR in the eyes of the west, although similar systems existed in the US at the same time, Solzhenitsin s numbers were exaggerated and most people were definitely just criminals. The soviets were sending kulaks (rich peasants that sabotaged soviet reforms) and other reported people (innocent) to distant parts of Siberia, but not into gulags, just regular settlements.