How did the Soviet Union incorporate Latvia in 1940?

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

The process unfolded through the following stages:

• Military Pressure: In October 1939, Latvia was forced to sign a treaty of mutual assistance, granting the U.S.S.R. military, naval, and air bases on its territory.12
• Invasion and Occupation: On June 17, 1940, the Red Army invaded and occupied the country.12
• Political Manipulation: On June 20, a new government was announced, and the Soviets organized elections where only a single list of candidates was permitted. During this time, President Kārlis Ulmanis was deported.12
• Formal Incorporation: On July 21, the newly elected Saeima voted to incorporate Latvia into the U.S.S.R. The Soviet Union officially accepted this incorporation on August 5, 1940.12

Following this annexation, a period known as the "year of terror" began, marked by the deportation of approximately 35,000 Latvians, particularly members of the intelligentsia, to prison camps in Siberia.12