The Soviet Union had its roots in the October Revolution of 1917 when the Bolsheviks, headed by Vladimir Lenin, overthrew the Provisional Government that had earlier replaced the monarchy of the Russian Empire. They established the Russian Soviet Republic, beginning a civil war between the Bolshevik Red Army and many anti-Bolshevik forces across the former Empire, among whom the largest faction was the White Guard, which engaged in violent anti-communist repression against the Bolsheviks and their worker and peasant supporters known as the White Terror. The Red Army expanded and helped local Bolsheviks take power, establishing soviets, repressing their political opponents and rebellious peasants through Red Terror. By 1922, the Bolsheviks had emerged victorious, forming the Soviet Union with the unification of the Russian, Transcaucasian, Ukrainian and Byelorussian republics. The New Economic Policy (NEP), which was introduced by Lenin, led to a partial return of a free market and private property; this resulted in a period of economic recovery.