How did the Soviet Union incorporate Estonia in 1940?

The incorporation of Estonia into the Soviet Union in 1940 was the result of a calculated process initiated by the German-Soviet Nonaggression Pact of 1939, which placed Estonia within the Soviet sphere of influence.123

The process unfolded through the following steps:

• Military Pressure: In September 1939, the Soviet Union forced Estonia to sign a treaty of mutual assistance, which allowed the Soviets to occupy several military bases within the country.12
• Ultimatum and Occupation: On June 16, 1940, the Soviet government issued an ultimatum demanding a new, compliant Estonian government. The following day, Soviet forces occupied the entire country.12
• Political Co-option: Under Soviet pressure, the Chamber of Deputies was presented with a resolution to join the U.S.S.R. on July 21, 1940. Despite the move being contrary to constitutional procedure, it was adopted the next day.12
• Formal Incorporation: On August 6, 1940, the Moscow Supreme Soviet officially incorporated Estonia as a constituent republic of the Soviet Union.12

During this period, many Estonian political leaders were arrested and deported, marking the beginning of widespread repression.12