Stalin transformed the Soviet Union into a totalitarian state by bringing all economic activity under strict government control, using terror and violence to eliminate opposition, and instituting total state control over all aspects of society. He imposed five-year plans to rapidly industrialize and collectivize agriculture, leading to tremendous growth but also famine and unrest. In response, Stalin purged millions of citizens and established an all-powerful secret police force and Gulag system to enforce absolute obedience through fear and oppression.