On this day - 17 June

The Soviet Union issued an ultimatum to Estonia on the afternoon of June 16th 1940 with a demand to answer by midnight that night. The ultimatum detailed allowing Soviet forces into Estonia and the creation of a new government. In an effort to avoid military action, Estonia signed. On June 17th 1940, Soviet forces entered Estonia and annexed the nation.

A similar situation occurred with neighbouring nation Latvia, which was also annexed by the Soviet Union on June 17th 1940 as they were not in a position to resist military offensive action from Soviet forces along the Latvian borders.