The Stalinist penal system was formed and entrenched during the 1930s—more precisely, between 1929 and 1941. Although its foundations had been laid earlier, the years 1929–30 were an important turning point, when the accelerated and intensive formation of Stalinist state structures, including the Gulag, began. The opening of war with Germany in 1941 logically ends this period.
Despite the apparent homogeneity of the prewar decade, historians have identified several distinct stages within it. For the most part, the history of the Gulag, and of repressive policy in general, follows that periodization.