Excerpts from Books and Wikipedia
"Essentially, the union was a re-creation of the old tsarist Russian Empire shorn of Poland and Finland, which had wrested their independence in a civil war following the 1917 Bolshevik Revolution. Always dominated by Russia, the USSR was initially composed of just four republics--Russia, Ukraine, Belorussia, and Transcaucasia--but as the Bolsheviks consolidated there control, more republics joined: Armenia, Azerbaijan, Georgia, Kazakhstan, Moldavia, Uzbekistan, Tajikistan, and Turkmenistan. In World War II, the Baltic republics of Estonia, Latvia, and Lithuania were forcibly annexed, too. . . . It extended communist control over Eastern Europe and communist influence across the entire world." [Furtado: 1001 Days]