The Union of Soviet Sovereign Republics (Russian: Союз Советских Cуверенных Республик, Soyuz Sovyetskikh Suvyeryennykh Ryespublik), known colloquially as the Soviet Union (Советский Союз, Sovyetskiy Soyuz), and abbreviated as the USSR (СССР, SSSR); is a country situated in northern Eurasia. A federation comprised of 21 republics, the USSR is the largest nation in area and one of the five global superpowers (along with the United States).
The Soviet Union was established in 1922, encompassing much of the territories of the former Russian Empire. The USSR became involved in World War II following Germany's invasion in 1941, eventually siding with the western allies. The Soviets suffered the largest casualties during the war, ending with the Soviet occupation of Berlin in 1945. Following the end of the war, the western allies and the USSR turned against each other for global economic and political. Known as the Cold War, the period was noted for the political dominance of the capitalist west (led by the United States) and the communist east (led by the Soviet Union), which was fought not by direct war but by manipulation, proxy-wars, and mutually assured destruction following the detonation of a Soviet nuclear bomb in 1949. The Cold War lasted from 1945 until 1990.
From its formation up until the 1980s the Soviet Union was a single-party communist state. Upon gaining power, Mikhail Gorbachev initiated economic and political reforms known as Perestroika and cultural reforms known as Glasnost. These reforms are credited with transforming the USSR into a more democratic and open nation, but also helped spark internal tensions. In 1991, the 20 republics helped to establish a decentralized federation of equal states. The 1990s saw the gradual revival of the Soviet Union domestically and acting as a model for all post-communist states. The 2000s brought the USSR back into global dominance following their involvement in the War on Terror and the Moscow metro bombings of 2003. Crimea was transfered back from Ukraine to Russia on February 23, 2014, with Novorossia promoted from a Autonomous Republic to a Republic on May 24.
Following World War II, the Soviet Union emerged as a global player in the arts, science, and sports. During the late 1950s and early 1960s, the USSR was the leading space power following the launches of Sputnik in 1957 and the flight of Yuri Gagarin in 1961. The Soviet Union continues to be a major player in the exploration of space.