Vincas Mickevičius-Kapsukas declared the formation of the Lithuanian Soviet Socialist Republic, a puppet state created by Soviet Russia to justify the Lithuanian–Soviet War.

Vincas Mickevičius, known under his pen name Kapsukas, was a Lithuanian communist political activist, publicist, and revolutionary.

The Lithuanian Soviet Socialist Republic (LSSR) was a short-lived Soviet puppet state during the early Interwar period. It was declared on 16 December 1918 by a provisional revolutionary government led by Vincas Mickevičius-Kapsukas. It ceased to exist on 27 February 1919, when it was merged with the Socialist Soviet Republic of Byelorussia to form the Lithuanian–Byelorussian Soviet Socialist Republic (Litbel) that itself lost control over all of its claimed territories by August 1919.

The Lithuanian–Soviet War or Lithuanian–Bolshevik War 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.