Following the capitulation of Germany in November 1918, the first Provisional Constitution of Lithuania was adopted and the first government of Prime Minister Augustinas Voldemaras was organized. At the same time, the army and other state institutions began to be organized. Lithuania fought three wars of independence: against the Bolsheviks who proclaimed the Lithuanian Soviet Socialist Republic, against the Bermontians, and against Poland. As a result of the staged Żeligowski's Mutiny in October 1920, Poland took control of Vilnius Region and annexed it as Wilno Voivodeship in 1922. Lithuania continued to claim Vilnius as its de jure capital and relations with Poland remained particularly tense and hostile for the entire interwar period. In January 1923, Lithuania staged the Klaipėda Revolt and captured Klaipėda Region (Memel territory) which was detached from East Prussia by the Treaty of Versailles. The region became an autonomous region of Lithuania.
In October 1939, Lithuania was forced to sign the Soviet-Lithuanian Mutual Assistance Treaty: five Soviet military bases with 20,000 troops were established in Lithuania in exchange for Vilnius that the Soviets captured from Poland. Delayed by the Winter War with Finland, the Soviets issued an ultimatum to Lithuania on 14 June 1940. They demanded to replace the Lithuanian government and to allow Red Army into the country. The government decided that with Soviet bases already in Lithuania armed resistance was impossible and accepted the ultimatum. President Smetona fled the country while more than 200,000 Soviet Red Army soldiers crossed the Belarus-Lithuania border. The next day, identical ultimatums were presented to Latvia and Estonia. The Baltic states were occupied. The Soviets followed semi-constitutional procedures for transforming the independent countries into soviet republics and incorporating them into the Soviet Union.
Vladimir Dekanozov was sent to supervise the formation of the puppet People's Government and the rigged election to the People's Seimas. The Lithuanian Soviet Socialist Republic was proclaimed on 21 July and accepted into the Soviet Union on 3 August.