Short answers, pulled from the story.
The Soviet Union and Germany signed a ten-year non-aggression pact on the 24th of August 1939. This agreement contained a secret protocol that assigned Finland, Estonia, Latvia, and Lithuania to the Soviet sphere of influence.
The Red Army occupied Lithuania on the 15th of June 1940 and occupied Latvia and Estonia on the 16th of June 1940. New popular front governments were formed in each country between the 18th and the 21st of June 1940 under Soviet surveillance.
Over half a million people were estimated to have been deported from the Baltic states between 1944 and 1952. The total included 124,000 from Estonia, 136,000 from Latvia, and 245,000 from Lithuania.
The Baltic Way took place on the 23rd of August 1989 as the biggest manifestation of opposition to Soviet rule. This event involved millions of citizens forming a human chain across Estonia, Latvia, and Lithuania to demand independence.
Lithuania declared independence on the 11th of March 1990 while Estonia made a similar declaration on the 30th of March 1990. Latvia followed suit by declaring the Soviet occupation illegal on the 4th of May 1990.
Russia completed the final withdrawal of troops from the region on the 31st of August 1994 after signing agreements for Latvia and Estonia in 1994. The last Russian soldier left the area in October 1999 when the Skrunda-1 radar station was decommissioned.