The Ukrainian Soviet Socialist Republic (Ukrainian: Українська Радянська Соціалістична Республіка, romanized: Ukrainska Radianska Sotsialistychna Respublika; Russian: Украинская Советская Социалистическая Республика), abbreviated as the Ukrainian SSR, UkSSR, and also known as Soviet Ukraine or just Ukraine, was one of the constituent republics of the Soviet Union from 1922 until 1991. Under the Soviet one-party model, the Ukrainian SSR was governed by the Communist Party of the Soviet Union through its republican branch, the Communist Party of Ukraine. The first iterations of the Ukrainian SSR were established during the Russian Revolution, particularly after the Bolshevik Revolution. The outbreak of the Ukrainian–Soviet War in the former Russian Empire saw the Bolsheviks defeat the independent Ukrainian People's Republic, during the conflict against which they founded the Ukrainian People's Republic of Soviets, which was governed by the Russian Soviet Federative Socialist Republic (RSFSR), in December 1917; it was later succeeded by the Ukrainian Soviet Republic in 1918. Simultaneously with the Russian Civil War, the Ukrainian War of Independence was being fought among the different Ukrainian republics founded by Ukrainian nationalists, Ukrainian anarchists, and Ukrainian separatists – primarily against Soviet Russia and the Ukrainian SSR, with either help or opposition from neighbouring states. In 1922, it was one of four Soviet republics (with the Russian SFSR, the Byelorussian SSR, and the Transcaucasian SFSR) that signed the Treaty on the Creation of the Soviet Union. As a Soviet quasi-state, the Ukrainian SSR became a founding member of the United Nations in 1945 alongside the Byelorussian SSR, in spite of the fact that they were also legally represented by the Soviet Union in foreign affairs. Upon the dissolution of the Soviet Union in 1991, the Ukrainian SSR emerged as the present-day independent state of Ukraine, although the modified Soviet-era constitution remained in use until the adoption of the modern Ukrainian constitution in June 1996.Throughout its 72-year history, the republic's borders changed many times, with a significant portion of what is now western Ukraine having been acquired via the Soviet-German Molotov–Ribbentrop Pact, with the annexation of Eastern Galicia and Volhynia in 1939, significant portions of Romania in 1940, alongside another annexation of territory in 1945 from Carpathian Ruthenia in Czechoslovakia. From the 1919 establishment of the Ukrainian SSR until 1934, the city of Kharkov served as its capital; however, the republic's seat of government was subsequently relocated in 1934 to the city of Kiev, the historic Ukrainian capital, and remained at Kiev for the remainder of its existence. Geographically, the Ukrainian SSR was situated in Eastern Europe, to the north of the Black Sea, and was bordered by the Soviet republics of Moldavia (since 1940), Byelorussia, and Russia, and the countries of Romania, Hungary, Czechoslovakia, and Poland. The republic's border with Czechoslovakia formed the Soviet Union's westernmost border point. According to the 1989 Soviet census, the republic of Ukraine had a population of 51,706,746 (second after Russia), which fell sharply after the Soviet Union's dissolution in 1991 due to high emigration rates, environmental pollution caused by the Chernobyl disaster of 1986 and male alcoholism. Source: Wikipedia (en)