Union of Soviet Socialist Republics (USSR) or Soviet Union, former republic, eastern Europe and northern and central Asia.
Area: 8,649,512 sq mi (22,402,235 sq km).
The USSR consisted, in its final years, of 15 soviet socialist republics that gained independence at its dissolution: Armenia, Azerbaijan, Belarus, Estonia, Georgia, Kazakhstan, Kyrgyzstan, Latvia, Lithuania, Moldova, Russia, Tajikistan, Turkmenistan, Ukraine, and Uzbekistan. It also contained 20 autonomous soviet socialist republics: 16 within Russia, 2 within Georgia, 1 within Azerbaijan, and 1 within Uzbekistan.
Stretching from the Baltic and Black seas to the Pacific Ocean, the Soviet Union comprised the largest country on the globe, having a maximum east-west extent of about 6,800 mi (10,900 km) and a maximum north-south extent of about 2,800 mi (4,500 km). It encompassed 11 time zones and had common boundaries with 6 European countries and 6 Asian countries.
Its regions contained fertile lands, deserts, tundra, high mountains, some of the world's largest rivers, and large inland waters, including most of the Caspian Sea. The coastline on the Arctic Ocean extended 3,000 mi (4,800 km), while that on the Pacific was 1,000 mi (1,600 km) long. The USSR was an agricultural, mining, and industrial power.
Following the Russian Revolution of 1917, four socialist republics were established on the territory of the former Russian Empire: the Russian Soviet Federated Socialist Republic, the Transcaucasian Soviet Federated Socialist Republic, the Ukrainian Soviet Socialist Republic, and the Belorussian Soviet Socialist Republic. These four constituent republics established the Union of Soviet Socialist Republics in 1922, to which other republics were added over the years.
A power struggle begun in 1924 with the death of communist leader Vladimir Lenin ended in 1927 when Joseph Stalin gained victory. Implementation of the first of the Five-Year Plans in 1928 centralised industry and collectivised agriculture. A purge in the late 1930s resulted in the imprisonment or execution of millions of persons considered dangerous to the state (see purge trials).
After World War II, with their respective allies, the USSR and the US engaged in the Cold War.
In the late 1940s the USSR helped to establish communist regimes throughout most of eastern Europe.
The USSR exploded its first atomic bomb in 1949 and its first hydrogen bomb in 1953.
Following Stalin's death, it experienced limited political and cultural liberalisation under Nikita Khrushchev.
It launched the first manned orbital spaceflight in 1961.
Under Leonid Brezhnev liberalisation was partially reversed.
In the mid-1980s Soviet leader Mikhail Gorbachev instituted liberal policies of glasnost and perestroika.
By the end of 1990 the communist government had toppled, and a program to create a market economy was implemented.
The USSR was officially dissolved on December 25, 1991.