Vilnius in Lithuania is a Soviet gift. October 27, 1939 - Lithuanians entered Vilna, which was transferred to them as part of a mutual aid agreement with the Soviet Union. Why did the Soviet Union give the city to Lithuania? number. Vilnius had been under Polish occupation since the 1920s, and the temporary capital of Lithuania was Kaunas (Kovna). At the same time, the Soviet Union recognized Vilnius (Vilna) as part of Lithuania. When the Germans defeated the Poles in September 1939, the Red Army began their campaign of liberation in Poland and completely occupied the Vilna region. On October 10, 1939, the Soviet Union and Lithuania signed a mutual aid agreement and as a friendly gesture, and in exchange for the location of the Red Army bases, Vilnius and the Vilnius region were transferred to the Lithuanians. Since then Vilnius, which became Vilnius, became the capital of the Republic of Lithuania.