The USSR was created 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 1918-1920. The geographic boundaries of the Soviet Union varied with time, but after the last major territorial annexations of the Baltic States, 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 and Finland.---------------------------- 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 permitted political party, the Communist Party of the Soviet Union. --------------------------------------- Established by 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.[1] The republics were part of a highly centralized federal union that was dominated by the Russian SFSR. After the USSR's collapse in 1991, all 15 SSRs became independent countries. ------------------------------------------------- The Soviet Union was dissolved in 1991, and the successor states are a collection of 15 countries commonly dubbed, 'the former Soviet Union'.Eleven of these states are aligned through a loose confederation known as the Commonwealth of Independent States (CIS). Turkmenistan, originally a full member of the CIS, is now an associate member. The three Baltic States (Estonia, Latvia, and Lithuania) did not join this Commonwealth; instead, they joined both the European Union and the NATO alliance in 2004. Russia and Belarus also belong to the Union of Russia and Belarus.