The Russian Civil War was a multi-party civil war in the former Russian Empire sparked by the overthrowing of the monarchy and the new republican government's failure to maintain stability, as many factions vied to determine Russia's political future. It resulted in the formation of the RSFSR 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 had been overthrown by the 1917 February Revolution, and Russia was in a state of political flux. A tense summer culminated in the Bolshevik-led October Revolution, overthrowing the Provisional Government of the Russian Republic. Bolshevik rule was not universally accepted, and the country descended into civil war. The two largest combatants were the Red Army, fighting for the Bolshevik form of socialism led by Vladimir Lenin, and the loosely allied forces known as the White Army, which included diverse interests favouring political monarchism, capitalism and social democracy, each with democratic and anti-democratic variants. In addition, rival militant socialists, notably the Ukrainian anarchists of the Makhnovshchina and Left Socialist-Revolutionaries, as well as non-ideological green armies, opposed the Reds, the Whites and foreign interventionists. Thirteen foreign nations intervened against the Red Army, notably the former Allied military forces from the World War with the goal of re-establishing the Eastern Front.