Crimea was historically under the control of the Russian Empire from 1783 to 1917 and Soviet Union from 1918 to 1991. Following the Russian Revolution of 1917 and the Russian Civil War (7 November 1917 – 25 October 1922), it was established in 1921 as the Crimean Autonomous Soviet Socialist Republic within the Russian Soviet Federative Socialist Republic in the USSR. During World War II, Crimea was downgraded to the Crimean Oblast after its entire indigenous population, the Crimean Tatars were deported to Central Asia, an act recognized as a genocide by Ukraine and 3 other countries. In 1954, it was transferred to the Ukrainian SSR from the Russian SFSR. Later, following a referendum on 20 January 1991, it was upgraded to the status of an autonomous republic within the Ukrainian SSR. When the Soviet Union collapsed in 1991 and Ukraine became an independent country, Crimea remained part of the newly independent Ukraine.