Soviet–Lithuanian Peace Treaty in the context of Soviet Belarus

The Byelorussian Soviet Socialist Republic (BSSR, Byelorussian SSR or Byelorussia; Belarusian: Беларуская Савецкая Сацыялістычная Рэспубліка; Russian: Белорусская Советская Социалистическая Республика), also known as Soviet Belarus or simply Belarus, was a republic of the Soviet Union (USSR). It existed between 1920 and 1922 as an independent state, and afterwards as one of fifteen constituent republics of the USSR from 1922 to 1991, with its own legislation from 1990 to 1991. The republic was ruled by the Communist Party of Byelorussia. It was also known as the White Russian Soviet Socialist Republic. Minsk was the capital and largest city of the republic.

Following the Treaty of Brest-Litovsk in March 1918, which ended Russia's involvement in World War I, the Belarusian Democratic Republic (BDR) was proclaimed under German occupation; however, as German troops left, the Socialist Soviet Republic of Byelorussia was established in its place by the Bolsheviks in December, and it was later merged with the Lithuanian Soviet Socialist Republic in 1919 to form the Socialist Soviet Republic of Lithuania and Belorussia, which ceased to exist as a result of the Polish occupation during the Polish–Soviet War. Following a peace treaty with Lithuania, the Socialist Soviet Republic of Byelorussia was re-founded on 31 July 1920 and later became known as the Byelorussian Soviet Socialist Republic.

Vilnius Region 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 Peace Treaty, 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.

The Lithuanian–Soviet War or Lithuanian–Bolshevik War (Lithuanian: karas su bolševikais) was fought between newly independent Lithuania and the Russian Socialist Federative Soviet Republic in the aftermath of World War I. It was part of the larger Soviet westward offensive of 1918–1919. The offensive followed the retreat of German troops and sought to establish Soviet republics in Ukraine, Belarus, Lithuania, Latvia, Estonia, and Poland, and to link up with the German Revolution. By the end of December 1918, Soviet forces reached Lithuanian borders. Largely unopposed, they occupied one town after another and by the end of January 1919, they controlled about two thirds of the Lithuanian territory. In February, the Soviet advance was stopped by Lithuanian and German volunteers, who prevented the Soviets from capturing Kaunas, the temporary capital of Lithuania. From April 1919, the Lithuanian war went parallel with the Polish–Soviet War. Poland had territorial claims over Lithuania, especially the Vilnius Region; these tensions spilt over into the Polish–Lithuanian War.

British-Polish historian Norman Davies summarized the situation: "the German army was supporting the Lithuanian nationalists, the Soviets were supporting the Lithuanian communists and the Polish Army was fighting them all." In mid-May, the Lithuanian army, now commanded by General Silvestras Žukauskas, began an offensive against the Soviets in Northeastern Lithuania. By mid-June, the Lithuanians reached the Latvian border and cornered the Soviets among lakes and hills near Zarasai, where the Soviets held out until the end of August 1919. The Soviets and Lithuanians, separated by the Daugava River, maintained their fronts until the Battle of Daugavpils in January 1920. As early as September 1919, the Soviets offered to negotiate a peace treaty, but talks began only in May 1920. The Soviet–Lithuanian Peace Treaty was signed on July 12, 1920. Soviet Russia fully recognized independent Lithuania.