The Union of Soviet Socialist Republics, also known as the Soviet Union or the USSR, was the world's largest and longest-lived socialist state. From 1922 to 1991, the USSR went through many changes, which included variations in border limits, territorial annexations, and political control. At the time of its creation in 1922, the USSR was a single unit that included Russia, Ukraine, and Belarus, along with the Transcaucasian Republics, which included Armenia, Georgia, and Azerbaijan.
Additional changes were made to the Soviet Union group throughout the year, until the final group was announced in 1956. By then, 15 countries had become part of the USSR: Armenia, Azerbaijan, Belarus, Estonia, Georgia, Kazakhstan, Kyrgyzstan, Latvia, Lithuania, Moldova, Russia, Tajikistan, Turkmenistan, Ukraine, and Uzbekistan. Russia was the most powerful of all the republics, and the one maintaining control over the territory and the main political decisions.
Until its fall in 1991, the Soviet Union covered 8,649,500 sq mi (22,402,200 square kilometers) and extended from the Arctic Ocean to the Afghan border. The 150 ethnic groups that formed the republic accounted for a total population of 293 million, most of whom lived in what is now Russia. Of the republics that were part of the Soviet Union, many were formed as new territories were acquired during the war, while others came to be when the central government decided to split an existing republic into two or more different zones.
The liberalization movements started by many of the republics were a major factor in the dissolution of the USSR. As perestroika came into effect, allowing the different republics to gain financial control of their own territories, the fractures of the republic became larger and larger. When the Soviet Union finally dissolved in 1991, Russia took responsibility for all debts, treaties, and properties that originally belonged to the Union. As the main executor during the Soviet Union period, Russia also became the one in charge of making political and financial decisions, including the political moves that gave birth to the Cold War.