On 23 August 1939 Germany and the Soviet Union signed the Molotov – Ribbentrop Pact . The pact 's secret protocol divided Eastern Europe into spheres of influence , with Estonia belonging to the Soviet sphere . On 24 September , the Soviet Union presented an ultimatum , demanding that Estonia sign a treaty of mutual assistance which would allow Soviet military bases into the country . The Estonian government felt that it had no choice but to comply , and the treaty was signed on 28 September . In May 1940 , Red Army forces in bases were set in combat readiness and , on 14 June , the Soviet Union instituted a full naval and air blockade on Estonia . On the same day , the airliner Kaleva was shot down by the Soviet Air Force . On 16 June , Soviets presented an ultimatum demanding completely free passage of the Red Army into Estonia and the establishment of a pro-Soviet government . Feeling that resistance was hopeless , the Estonian government complied and , on the next day , the whole country was occupied . On 6 August 1940 , Estonia was annexed by the Soviet Union as the Estonian SSR . The German government initiated a program to relocate most of Estonia 's Baltic German population to the land of the ancestors
Kaleva
Kaleva (airplane)
Estonia