World War II: The Soviet Union invades East Karelia and the previously Finnish part of Karelia, occupied by Finland since 1941.

The Soviet Union, officially the Union of Soviet Socialist Republics (USSR), 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, the largest by area, and bordered twelve countries. A diverse multinational state, it was organized as a federal union of national republics, with the largest and most populous being the Russian SFSR. 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.