1936–1938 campaign in the Soviet Union
Source (Wikipedia): Great Purge

The Great Purge, or the Great Terror, also known as the Year of ‘37 and the Yezhovshchina, was a political purge in the Soviet Union that took place from 1936 and 1938. It sought to consolidate Joseph Stalin’s power over the Communist Party of the Soviet Union and aimed at removing the remaining influence of Leon Trotsky within the Soviet Union. The term great purge was popularized by the historian Robert Conquest in his 1968 book The Great Terror, whose title was an allusion to the French Revolution’s Reign of Terror.