The Union of Soviet Socialist Republics () abbreviated to USSR () or shortened to the Soviet Union (), was a Marxist–Leninist state on the Eurasian continent that existed between 1922 and 1991. A union of multiple subnational Soviet republics, its government and economy were highly centralized. The Soviet Union was a single-party state, governed by the Communist Party with Moscow as its capital.
The Soviet Union had its roots in 1917 when the Bolsheviks, headed 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, which 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 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 foundation for its victory in World War II and post-war dominance. Stalin also fomented political paranoia, and conducted the Great Purge to remove opponents of his from the Communist Party through the mass arbitrary arrest of many people (military leaders, Communist Party members, and ordinary citizens alike) who were then sent to correctional labour camps or sentenced to death.
In the beginning of World War II, Stalin signed a non-aggression pact with Hitler's Germany; the treaty delayed confrontation between the two countries. In June 1941 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 Stalingrad. Soviet forces eventually captured Berlin in 1945. The territory overtaken by the Red Army became satellite states of the Eastern Bloc. The Cold War emerged in 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 so-called "hot wars."
Following Stalin's death in 1953, a period of political and economic liberalization, known as "de-Stalinization" and "Khrushchev's Thaw", occurred under the leadership of Nikita Khrushchev. The country grew rapidly, as millions of peasants were moved into industrialized cities. The Space Race heated up, and the USSR took an early lead with the first ever satellite and world's first human spaceflight. In the 1970s, there was, briefly, a ''détente'' of relations with the United States, 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 aid to Mujahideen fighters.
In the mid-1980s, the last Soviet leader, Mikhail Gorbachev, sought to further reform and liberalize the economy through his policies of ''glasnost'' and ''perestroika''. The goal was to preserve the Communist Party while reversing economic stagnation. The Cold War ended during his tenure, and in 1989 Soviet satellite countries in Eastern Europe overthrew their respective communist regimes. This led to the rise of strong nationalist and separatist movements inside the USSR as well. 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 August 1991, a coup d'état was attempted by Communist Party hardliners. It failed, with Russian President Boris Yeltsin playing a high-profile role in facing down the coup, resulting in the banning of the Communist Party. On 25 December 1991, Gorbachev resigned and the remaining twelve constituent republics emerged from the dissolution of the Soviet Union as independent post-Soviet states. The Russian Federation (formerly the Russian SFSR) assumed the Soviet Union's rights and obligations and is recognized as its continued legal personality.
== Geography, climate and environment ==
(詳細はworld's largest country, a status that is retained by the Russian Federation.〔(Russia - Encyclopedia Britannica ). Britannica.com (27 April 2010). Retrieved on 29 July 2013.〕 Covering a sixth of Earth's land surface, its size was comparable to that of North America.〔http://pages.towson.edu/thompson/courses/regional/reference/sovietphysical.pdf〕 The European portion accounted for a quarter of the country's area, and was the cultural and economic centre. The eastern part in Asia extended to the Pacific Ocean to the east and Afghanistan to the south, and, except some areas in Central Asia, was much less populous. It spanned over east to west across 11 time zones, and over north to south. It had five climate zones: tundra, taiga, steppes, desert, and mountains.
The Soviet Union had the world's longest border, like Russia, measuring over , or circumferences of Earth. Two-thirds of it was a coastline. Across the Bering Strait was the United States. The Soviet Union bordered Afghanistan, China, Czechoslovakia, Finland, Hungary, Iran, Mongolia, North Korea, Norway, Poland, Romania, and Turkey from 1945 to 1991.
The Soviet Union's highest mountain was Communism Peak (now Ismoil Somoni Peak) in Tajikistan, at . The Soviet Union also included most of the world's largest lake, the Caspian Sea (shared with Iran), and also Lake Baikal, the world's largest freshwater and deepest lake, an internal body of water in Russia.
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