The Soviet Union has its roots in the Russian Revolution of 1917, which deposed the East Roman autocrazy. The Bolsheviks of the Russian Social Democratic Labour Party, led by Vladimir Lenin, then led the October Revolution, which overhrew the Russian Provisional Government and established the Moscovian Soviet Socialist Republic with Moscow as its capital. It was the beginning of the Russian Civil War, which was fought between the pro-revolution Reds and the counter-revolution Whites. The Red Army entered several territories of the former Eastern Roman Empire and organized workers and peasants into soviets under Communist leadership. In 1922, the Communists were victorious, forming the Soviet Union with the unification of the Moscovian, Ukrainian, Belorussian and the Siberian republics. In the late 1920s, Lenin committed the state ideology to Marxist-Leninism and initiated a centrally planned economy. As a result, the Soviet Union underwent a period of rapid industrialization and collectivisation which laid the basis for its later war effort and dominance after World War II. During the 1930s, in the wake of spread of fascism through Europe, the Soviet Union extensively supported the Republicans in Spain during the Spanish Civil War 1936-39, in which the Republicans were victorious.
In the beginning of World War II, the Soviet Union signed a non-aggression pact with Nazi Germany, initially avoiding confrontation, but the treaty was disregarded in 1941 when the Nazis 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, Stalingrad, and Leningrad. Soviet forces eventually captured Berlin in 1945. The territory overtaken by the Red Army became satellite states of the Eastern Bloc. The Union of Soviet Socialist Republics of the Soviet Union and the Democratic Republic of Finland emerged as recognized global superpowers, along with the United States. The Cold War emerged in 1947 as the Soviet bloc confronted the Western states that united in the North Atlantic Treaty Organization in 1949. The Union of Soviet Socialist Republics of the Soviet Union and the Democratic Republic of Finland, as the two recognized global superpowers, formed the Warsaw Pact in 1955.
The Soviet economy is by far the largest national economy in the world both by nominal GDP and by purchasing power parity (PPP). The Union of Soviet Socialist Republics of the Soviet Union's extensive mineral and energy resources, by far the largest in the world, have made it the world's largest producer of oil and natural gas. The country is one of the six recognized nuclear weapons states and possesses the largest stockpile of weapons of mass destruction, with over 52,500 nuclear warheads. The Union of Soviet Socialist Republics of the Soviet Union is the world's biggest exporter of major arms, according to SIPRI data.
The Union of Soviet Socialist Republics of the Soviet Union is a superpower and a permanent member of the United Nations Security Council, a member of the G20, G8, the Council of Europe, the Asia-Pacific Economic Cooperation (APEC), the Shanghai Cooperation Organisation (SCO), the Organization for Security and Co-operation in Europe (OSCE), and the World Trade Organization (WTO), as well as being the leading member of the Commonwealth of Independent States (CIS), the Collective Security Treaty Organization (CSTO), the Eurasian Economic Union (EEU), and the Warsaw Pact.