The Russian Civil War (1917--1921) was a multi-party war that occurred within the former Russian Empire after the Russian provisional government collapsed and the Soviets under the domination of the Bolshevik party assumed power, first in Petrograd (St. Petersburg) and then in other places.
The principal fighting occurred between the Bolshevik Red Army, often in temporary alliance with other leftist pro-revolutionary groups, and the forces of the White Army, the loosely-allied anti-Bolshevik forces. Many foreign armies warred against the Red Army, notably the Allied Forces, and many volunteer foreigners fought in both sides of the Russian Civil War. The Polish--Soviet War is often viewed as a theatre of the conflict. Other nationalist and regional political groups also participated in the war, including the Ukrainian nationalist Green Army, the Ukrainian anarchist Black Army and Black Guards, and warlords such as Ungern von Sternberg.