The Great Purge or the Great Terror was Soviet General Secretary Joseph Stalin's campaign to solidify his power over the party and the state; the purges were also designed to remove the remaining influence of Leon Trotsky as well as other prominent political rivals within the party. Following the death of Vladimir Lenin in 1924 a power vacuum opened in the Communist Party. Various established figures in Lenin's government attempted to succeed him. Joseph Stalin, the party's General Secretary, outmaneuvered political opponents and ultimately gained control of the Communist Party by 1928. Initially, Stalin's leadership was widely accepted; his main political adversary Trotsky was forced into exile in 1929, and the doctrine of "socialism in one country" became enshrined party policy. However, by the early 1930s, party officials began losing faith in his leadership following the human cost of the First Five Year Plan and Soviet collectivization of agriculture. By 1934 several of Stalin's rivals, such as Trotsky, began calling for Stalin's removal and attempted to break his influence over the party.

By 1936, Stalin's paranoia reached a crescendo. The fear of losing his position and the potential return of Trotsky drove him into authorizing the Great Purge. The purges themselves were largely conducted by the NKVD (People's Commissariat for Internal Affairs), the secret police of the USSR. The NKVD began the removal of the central party leadership, Old Bolsheviks, government officials, and regional party bosses. Eventually, the purges were expanded to the Red Army and military high command, which had a disastrous effect on the military altogether. Three successive trials were held in Moscow that removed most of the Old Bolsheviks and challenges to Stalin's legitimacy. As the scope of the purge began widening, the omnipresent suspicion of saboteurs and counter-revolutionaries began impacting civilian life. The NKVD began targeting certain ethnic minorities such as the Volga Germans, who were subjected to forced deportation and extreme repression. During the purge, the NKVD widely utilized imprisonment, torture, violent interrogation, and arbitrary executions to solidify control over civilians through fear.

In 1938, Stalin reversed his stance on the purges and declared that the internal enemies had been removed. Stalin criticized the NKVD for carrying out mass executions and subsequently executed Genrikh Yagoda and Nikolai Yezhov, who headed the NKVD during the purge years. Despite the Great Purge being over, the atmosphere of mistrust and widespread surveillance continued for decades after. Scholars estimate the death toll for the Great Purge (1936–1938) to be roughly 700,000.