How many countries were part of the USSR?
At different times, the number of countries (called Union republics) that were part of the Union of Soviet Socialist Republics (USSR) varied.
At the time of the collapse of the USSR in 1991 there were 15 Union republics:
Russian Soviet Federal socialist Republic (RSFSR),
The Ukrainian SSR
The Uzbek SSR
The Turkmen SSR
The Latvian SSR
The Estonian SSR
From 1940 to 1956, there was the Karelo-Finnish SSR (now the Republic of Karelia in the Russian Federation).
Georgia, Armenia, and Azerbaijan were part of the Transcaucasian Soviet Federal Socialist Republic (ZSFSR) from 1922 to 1937.
Occupying a sixth of the land area (22,400,000 km2), the USSR was the largest state in the world and had the longest border in the world (more than 60,000 kilometers).
Between 1945 and 1991, the Soviet Union bordered 14 States: China, Mongolia, North Korea, Japan, Turkey, Iran, Afghanistan, the United States, Hungary, Romania, Czechoslovakia, Norway, Poland, and Finland.