Vilnius Region

Vilnius Region^[a] is the territory in present-day Lithuania and Belarus that was originally inhabited by ethnic Baltic tribes and was a part of Lithuania proper, but came under East Slavic and Polish cultural influences over time.

The territory included Vilnius, the historical capital of the Grand Duchy of Lithuania. Lithuania, after declaring independence from the Russian Empire, claimed the Vilnius Region based on this historical legacy. Poland argued for the right of self-determination of the local Polish-speaking population. As a result, throughout the interwar period the control over the area was disputed between Poland and Lithuania. The Soviet Union recognized it as part of Lithuania in the Soviet-Lithuanian Treaty of 1920, but in 1920 it was seized by Poland and became part of the short-lived puppet state of Central Lithuania, and was subsequently incorporated into the Second Polish Republic.

Direct military conflicts (Polish–Lithuanian War and Żeligowski's Mutiny) were followed up by fruitless negotiations in the League of Nations. After the Soviet invasion of Poland in 1939, as part of the Soviet fulfilment of the Molotov–Ribbentrop Pact, the entire region was occupied by the Soviet Union. About one-fifth of the region, including Vilnius, was ceded to Lithuania by the Soviet Union on 10 October 1939 in exchange for Soviet military bases within the territory of Lithuania as part of the Soviet–Lithuanian Mutual Assistance Treaty. The remaining part of the region was given to the Byelorussian Soviet Socialist Republic.

The conflict over Vilnius Region was settled after World War II when both Poland and Lithuania were in the Eastern Bloc, as Poland was the Soviet satellite state of the Polish People's Republic and Lithuania was occupied by the Soviet Union as the Lithuanian Soviet Socialist Republic, and Poles were repatriated to Poland. From the late 1940s to 1990, the region was divided between the Lithuanian SSR and Byelorussian SSR, and since 1990 between modern-day independent Lithuania and Belarus.