Nazi Germany, under Adolph Hitler, maintained concentration camps intended to hold political prisoners and opponents of the regime. They grew rapidly through the 1930s as political opponents and many other groups of people were incarcerated without trial or judicial process. Concentration camps are distinct from extermination camps, which were established for the sole purpose of carrying out the extermination of the Jews of Europe. Concentration camps were established in the Soviet Union following the 1917 revolution and proliferated during the Stalin era. These forced labor camps are often referred to by the acronym GULAG, for the Soviet bureaucratic institution which operated them, Glavnoe Upravlenie ispravitel’no-trudovykh LAGerei.