World War II: Soviet and Bulgarian forces capture Vienna.

The Union of Soviet Socialist Republics (USSR), also known as the Soviet Union, was a transcontinental country that spanned much of Eurasia from 1922 until its dissolution in 1991. It was the world's third-most populous country, largest by area, and bordered twelve countries. A diverse multinational state, it was organized as a federal union of national republics, the largest and most populous being the Russian Soviet Federative Socialist Republic. In practice, its government and economy were highly centralized. As a one-party state governed by the Communist Party, it was the flagship communist state. Its capital and largest city was Moscow.