Lithuanian Soviet Socialist Republic (1918–19) in the context of Vincas Mickevičius-Kapsukas

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.