The Russian Civil War (Russian: Гражданская война в России, romanized: Grazhdanskaya voyna v Rossii) was a multi-party civil war in the former Russian Empire sparked by the 1917 overthrowing of the Russian Provisional Government in the October Revolution, as many factions vied to determine Russia's political future. It resulted in the formation of the Russian Socialist Federative Soviet Republic and later the Soviet Union in most of its territory. Its finale marked the end of the Russian Revolution, which was one of the key events of the 20th century.
The Russian monarchy ended with the abdication of Tsar Nicholas II during the February Revolution, and Russia was in a state of political flux. A tense summer culminated in the October Revolution, where the Bolsheviks overthrew the provisional government of the new Russian Republic. Bolshevik seizure of power was not universally accepted, and the country descended into a conflict which became a full-scale civil war in May–June 1918. The two largest combatants were the Red Army, fighting for the establishment of a Bolshevik-led socialist state headed by Vladimir Lenin, and the forces known as the White movement (and its White Army), led mainly by the right-leaning officers of the Russian Empire, united around the figure of Alexander Kolchak. In addition, rival militant socialists, notably the Ukrainian anarchists of the Makhnovshchina and Left Socialist-Revolutionaries, were involved in conflict against the Bolsheviks. They, as well as non-ideological green armies, opposed the Bolsheviks, the Whites and the foreign interventionists. Thirteen foreign states intervened against the Red Army, notably the Allied intervention, whose primary goal was re-establishing the Eastern Front of World War I. Three foreign states of the Central Powers also intervened, rivaling the Allied intervention with the main goal of retaining the territory they had received in the Treaty of Brest-Litovsk with Soviet Russia.