The Soviet Union, officially the Union of Soviet Socialist Republics (USSR), was formally established in December 1922.

It was created through a treaty between the Russian Soviet Federative Socialist Republic and other Soviet republics.

The founding republics were Russia, Ukraine, Belorussia (Belarus), and the Transcaucasian Federation (which later split into Georgia, Armenia, and Azerbaijan).

The USSR was theoretically a voluntary federation of equal republics.

In practice, it was a highly centralized state, dominated by the Russian Republic and ruled by the Communist Party in Moscow.

The constitution of the USSR was based on the principle of the 'dictatorship of the proletariat.'

Over time, the number of constituent republics grew as Central Asian and other territories were incorporated.

The capital of the Soviet Union was Moscow.

The formation of the USSR solidified the Bolsheviks' control over the former territories of the Russian Empire.

The Soviet Union existed for nearly 70 years until its dissolution in 1991.