European-Asian communist federation that lasted from 1924 to 1991 and comprised of 12 main republics (Armenia, Azerbaijan, Belarus, Georgia, Kazakhstan, Kirgizstan, Moldova, Russia, Tajikistan, Turkmenistan, Ukraine, and Uzbekistan) and three Baltic republics (Estonia, Latvia, and Lithuania). Then also called Soviet (from Russian 'sovet,' council) Union, it was the largest state in the world and had a population of some 300 million. Now called Former Soviet Union (FSU).