During World War II, the Soviet Union occupied and annexed several countries allocated to it in the secret Molotov–Ribbentrop Pact of 1939. These included the eastern regions of Poland (incorporated into three different SSRs), as well as Latvia (became Latvian SSR), Estonia (became Estonian SSR), Lithuania (became Lithuanian SSR), part of eastern Finland (became Karelo-Finnish SSR) and eastern Romania (became the Moldavian SSR and part of Ukrainian SSR). Apart from the Molotov–Ribbentrop Pact and post-war division of Germany, the Soviets also occupied and annexed Carpathian Ruthenia from Czechoslovakia in 1945 (became part of Ukrainian SSR). These occupations lasted until the dissolution of the Soviet Union in 1990 and 1991.
Below is a list of various forms of military occupations by the Soviet Union resulting from both the Soviet pact with Nazi Germany (ahead of World War II), and the ensuing Cold War in the aftermath of Allied victory over Germany.