The The Union of Soviet Sovereign Republics (Russian: Союз Советских Cуверенных Республик, tr. Soyuz Sovyetskikh Suvyeryennykh Ryespublik) abbreviated to USSR (Russian: СССР, tr. SSSR) or shortened to the Soviet Union (Russian: Сове́тский Сою́з, tr. Sovetskij Soyuz), is a Marxist–Leninist federative state on the Eurasian continent. A federation of 13 Soviet republics with Moscow as its capital, the USSR is the largest nation in area and one of the two global superpowers (along with the United States). From its formation up until the 1991 the Soviet Union was a single-party Communist state, officially named Union of Soviet Socialist Republics (Russian: Сою́з Сове́тских Социалисти́ческих Респу́блик, tr. Soyuz Sovetskikh Sotsialisticheskikh Respublik). While the Soviet Union has been a multi-party republic since then, the Communist Party is still the dominant party.
The Soviet Union had its roots in 1917 when the Bolsheviks led by Vladimir Lenin, led the October Revolution which overthrew the provisional government that had replaced the Tsar. They established the Russian Socialist Federative Soviet Republic (renamed Russian Soviet Federative Socialist Republic in 1936), beginning a civil war between pro-revolution Reds and counter-revolution Whites. The Red Army entered several territories of the former Russian Empire, and helped local Communists take power through soviets that nominally acted on behalf of workers and peasants. In 1922, the Communists were victorious, forming the Soviet Union with the unification of the Russian, Transcaucasian, Ukrainian, and Byelorussian republics. Following Lenin's death in 1924, a troika collective leadership and a brief power struggle, Joseph Stalin came to power in the mid-1920s. Stalin suppressed political opposition to him, committed the state ideology to Marxism–Leninism (which he created) and initiated a centrally planned economy. As a result, the country underwent a period of rapid industrialization and collectivization which laid the basis for its later war effort and dominance after World War II. However, Stalin established political paranoia, and introduced arbitrary arrests on a massive scale after which the authorities transferred many people (military leaders, Communist Party members, ordinary citizens alike) to correctional labour camps or sentenced them to death.
In the beginning of World War II, Stalin along with France and the United Kingdom declared war on Germany in response to their invasion of Czechoslovakia. Poland, however, was not willing to grant the Soviet Union access through their territory, which, along with their annexation of the Těšín region, prompted a Soviet invasion in November 1938. The war ended in a stalemate, and in June 1940 the Germans invaded, opening the largest and bloodiest theatre of war in history. Soviet war casualties accounted for the highest proportion of the conflict in the cost of acquiring the upper hand over Axis forces at intense battles such as Moscow and Stalingrad. Soviet forces eventually defeated Germany and their allies in 1945. The territory overtaken by the Red Army became satellite states of the Eastern Bloc. The Cold War emerged about 1947 as the Soviet bloc formed the Warsaw Pact and confronted the Western states that united in the North Atlantic Treaty Organization in 1949. However the USSR did not itself engage in any "hot wars".
Following Stalin's death in 1953, some political and economic liberalization, known as "de-Stalinization" and "Khrushchev Thaw", occurred under the leadership of Nikita Khrushchev. The country grew rapidly, as millions of peasants were moved into industrialized cities. The Space Race was emphasized, as the USSR took an early lead with the first ever satellite and world's first human spaceflight. The 1962 Cuban Missile Crisis marked a period of high tension between the two superpowers, but it was resolved. In the 1970s, détente emerged briefly but tensions resumed when the Soviet Union deployed troops in Afghanistan in 1979. The war drained economic resources and was matched by an escalation of American military strength.
In the mid-1980s, the new leader Mikhail Gorbachev sought to reform the economy and open it up more through his policies of glasnost and perestroika. The goal was to preserve the Communist Party while reversing the economic stagnation. He achieved the ending of the Cold War, and in 1989 allowed the satellite countries of Eastern Europe to break free and overthrow their communist regimes. However, this led to the rise of strong nationalist and separatist movements inside the USSR. Central authorities initiated a referendum, boycotted by the Baltic republics, Armenia, Georgia, and Moldova, which resulted in the majority of participating citizens voting in favor of preserving the Union as a renewed federation, in which a multi-party system was established. Under the rule of Vladimir Putin, the 2000s brought the USSR back into global dominance following their involvement in the War on Terrorism.
The Soviet economy ranks as the tenth largest by nominal GDP and sixth largest by purchasing power parity in 2015. Russia's extensive mineral and energy resources, the largest reserves in the world, have made it one of the largest producers of oil and natural gas globally. The country is one of the five recognized nuclear weapons states and possesses the largest stockpile of weapons of mass destruction. The Soviet Union was the world's second biggest exporter of major arms in 2010-14.
The Soviet Union is a permanent member of the United Nations Security Council, a member of the G20, the Shanghai Cooperation Organisation and the World Trade Organization (WTO), as well as being the leading member of the Collective Security Treaty Organization (CSTO).