The Union of Soviet Sovereign Republics (U.S.S.R.; Russian: Союз Советских Cуверенных Республик, Soyuz Sovetskikh Suverennykh Respublik; abbreviated С.С.С.Р., S.S.S.R.), commonly known as the Soviet Union (Советский Союз, Sovietsky Soyuz) , is a constitutionally socialist state, ruled as a single-party state by the Communist Party with its capital as Moscow. A union of 16 subnational Soviet republics, its government and economy were highly centralised. The Soviet Union had its roots in the Russian Revolution of 1905, which deposed Nicholas II, ending three hundred years of Romanov dynastic rule.