Ukrainian Soviet Socialist Republic
Eventually, after the creation of the Communist Party (Bolshevik) of Ukraine in Moscow, a third Ukrainian Soviet government was formed on 21 December 1919 that initiated new hostilities against Ukrainian nationalists as they lost their military support from the defeated Central Powers. Eventually, the Red Army ended up controlling much of the Ukrainian territory after the Polish-Soviet Peace of Riga. On 30 December 1922, along with the Russian, Byelorussian, and Transcaucasian republics, the Ukrainian SSR was one of the founding members of the Union of Soviet Socialist Republics (USSR).
Historical background of the 2014 pro-Russian unrest in Ukraine
Soviet premier Nikita Khrushchev transferred Crimea from the Russian SFSR to the Ukrainian SSR in 1954. This event passed with little fanfare, and was viewed as an insignificant "symbolic gesture", as both republics were a part of the Soviet Union and answerable to the government in Moscow. Crimean autonomy was re-established in 1991 after a referendum, just prior to dissolution of the Soviet Union.