The young Republic of Lithuania felt more and more threatened not starting with the Begin of World War II, and for good reason. In March 1939, they already were forced to give back Memel to Germany. But what's worse, even if they don't know it: In the secret Molotov-Ribbentrop Pact the Soviet Union got the Baltic States promised by Nazi Germany. As a consequence, the Soviet Union forced Lithuania in early October 1939, to sign a "mutual assistance pact" with them - which allowed the Soviets to create Military bases in Lithuania. The fact that both sides had a non-aggression pact with Germany didn't help them. At least on October 10th, the SU gave the Vilnius (the old capital) area back to Lithuania, which Poland had annexed earlier in 1922. On June 8th in 1940, they received an ultimatum; two days later, the country was occupied.