Виленский край
In 1939, the Soviets proposed to sign the Soviet–Lithuanian Mutual Assistance Treaty. According to this treaty, about one fifth of the Vilnius Region, including the city of Vilnius itself, was returned to Lithuania in exchange for stationing 20,000 of Soviet troops in Lithuania. Lithuanians at first did not want to accept this, but later the Soviet Union said that troops would enter Lithuania, anyway, so Lithuania accepted the deal. 1/5 of the Vilnius region was ceded, despite of the fact that the Soviet Union always recognised the whole Vilnius region as part of Lithuania previously.