The Great Purge (1936-1938)

Stalin destroyed potential rivals through a wave of arrests, show trials, and executions. Old Bolsheviks who had served with Lenin were tried for fantastic crimes and executed. The military officer corps was decimated (with consequences in 1941 when Germany invaded). An estimated 700,000 to 1.2 million people were executed; millions more were sent to the Gulag system of forced labor camps. The NKVD (secret police) became one of the most feared institutions in the world.