The period of Soviet history from Lenin's death through Stalin's own death — encompassing forced collectivization, industrialization, the Great Terror, the Second World War, and the Cold War's beginning — during which the USSR became an industrial superpower and a totalitarian state responsible for millions of deaths.
Stalin industrialized a peasant country in a decade. He defeated Hitler. He built a nuclear bomb. He also killed millions of his own citizens through famine, purge, and the Gulag. Both things are true. Understanding Stalinism means holding the achievement and the atrocity in the same frame.