The Soviet Union, officially the Union of Soviet Socialist Republics (USSR), was a transcontinental country spanning much of Eurasia that existed from 30 December 1922 to 26 December 1991. A flagship communist state, it was nominally a federal union of fifteen national republics; in practice, both its government and its economy were highly centralized until its final years. It was a one-party state governed by the Communist Party of the Soviet Union, with the city of Moscow serving as its capital as well as that of its largest and most populous republic: the Russian SFSR. Other major cities included Leningrad (Russian SFSR), Kiev (Ukrainian SSR), Minsk (Byelorussian SSR), Tashkent (Uzbek SSR), Alma-Ata (Kazakh SSR), and Novosibirsk (Russian SFSR). It was the largest country in the world, covering over and spanning eleven time zones. The country's roots lay in the October Revolution of 1917, which saw the Bolsheviks, overthrow the Russian Provisional Government that formed earlier that year following the February Revolution and the abdication of Tsar Nicholas II, marking the end of the Russian Empire. Following the coup, the Bolsheviks lead by Vladimir Lenin established the Russian Socialist Federative Soviet Republic (RSFSR), the world's first constitutionally guaranteed socialist state. Persisting internal tensions escalated into the brutal Russian Civil War. As the war progressed in the Bolshevik's favor, the RSFSR began to incorporate land conquered from the war into nominally independent states, which were unified into the Soviet Union in December 1922. Following Lenin's death in 1924, Joseph Stalin came to power. Stalin inaugurated a period of rapid industrialization and forced collectivization that led to significant economic growth, but also contributed to a famine in 1930–1933 that killed millions. The labour camp system of the Gulag was also expanded in this period. Stalin conducted the Great Purge to remove his actual and perceived opponents. After the outbreak of World War II, Germany invaded the Soviet Union. The combined Soviet civilian and military casualty count—estimated to be around 27 million people—accounted for the majority of losses of Allied forces. In the aftermath of World War II, the territory taken by the Red Army formed various Soviet satellite states. The beginning of the Cold War saw the Eastern Bloc of the Soviet Union confront the Western Bloc of the United States, with the latter grouping becoming largely united in 1949 under NATO and the former grouping becoming largely united in 1955 under the