The Union of Soviet Socialist Republics also called the Soviet Union (Russian: ????´????? ???´?; tr.: Sovetskiy Soyuz), was a constitutionally socialist state that existed in Eurasia from 1922 to 1991. It was often incorrectly, and sometimes intentionally, referred to as Russia after its largest and dominant constituent state. From 1945 until its dissolution in 1991 — a period known as the Cold War—the Soviet Union and the United States of America were the two world superpowers that dominated the global agenda of economic policy, foreign affairs, military operations, cultural exchange, scientific advancements including the pioneering of space exploration, and sports (including the Olympic Games and various world championships).-------------------------The USSR was born and expanded as a union of Soviet republics formed within the territory of the Russian Empire abolished by the Russian Revolution of 1917 followed by the Russian Civil War of 1918–1921. The geographic boundaries of the Soviet Union varied with time, but after the last major territorial annexations and occupation of the Baltic states (Lithuania, Latvia, and Estonia), eastern Poland, Bessarabia, and certain other territories during World War II, from 1945 until dissolution the boundaries approximately corresponded to those of late Imperial Russia, with the notable exclusions of Poland, most of Finland, and Alaska. ------------------------------------- The Soviet Union became the primary model for future Communist states during the Cold War; the government and the political organization of the country were defined by the only political party, the Communist Party of the Soviet Union. ------------------------------------ Initially established as a union of four Soviet Socialist Republics, the USSR grew to contain 15 constituent or "union republics" by 1956: Armenian SSR, Azerbaijan SSR, Byelorussian SSR, Estonian SSR, Georgian SSR, Kazakh SSR, Kyrgyz SSR, Latvian SSR, Lithuanian SSR, Moldavian SSR, Russian SFSR, Tajik SSR, Turkmen SSR, Ukrainian SSR, and Uzbek SSR. (From annexation of Estonian SSR on August 6, 1940 up to reorganization of Karelo-Finnish SSR into Karelian ASSR on July 16, 1956, the official count of "union republics" was 16.) The republics were part of a highly centralized federal union that was dominated by the Russian SFSR.