During the second half of the 1920s, Joseph Stalin set the stage for gaining absolute power by employing police repression against opposition elements within the Communist Party. The machinery of coercion had previously been used only against opponents of Bolshevism, not against party members themselves. The first victims were Politburo members Leon Trotskii, Grigorii Zinov'ev, and Lev Kamenev, who were defeated and expelled from the party in late 1927. Stalin then turned against Nikolai Bukharin, who was denounced as a "right opposition," for opposing his policy of forced collectivization and rapid industrialization at the expense of the peasantry.
Stalin had eliminated all likely potential opposition to his leadership by late 1934 and was the unchallenged leader of both party and state. Nevertheless, he proceeded to purge the party rank and file and to terrorize the entire country with widespread arrests and executions. During the ensuing Great Terror, which included the notorious show trials of Stalin's former Bolshevik opponents in 1936-1938 and reached its peak in 1937 and 1938, millions of innocent Soviet citizens were sent off to labor camps or killed in prison.
By the time the terror subsided in 1939, Stalin had managed to bring both the party and the public to a state of complete submission to his rule. Soviet society was so atomized and the people so fearful of reprisals that mass arrests were no longer necessary. Stalin ruled as absolute dictator of the Soviet Union throughout World War II and until his death in March 1953.