Short answers, pulled from the story.
The Soviet Union annexed Bessarabia and Northern Bukovina on the 28th of June 1940 after presenting an ultimatum to Romania. This action followed a secret protocol in the Molotov-Ribbentrop Pact signed on the 23rd of August 1939 that assigned these regions to the Soviet sphere of interest.
A local assembly called Sfatul țării declared the Moldavian Democratic Republic on the 15th of December 1917. This declaration occurred during the 1917 Russian Revolution before Romanian troops entered the region in early January 1918.
In June 1941 alone, 31,699 people were deported from Soviet Moldova to Siberia. An additional 8,374 Romanians were deported from Chernivtsi oblast and 3,767 from Izmail oblast, totaling 43,840 deportees that month.
Between late 1941 and early 1944, Romania occupied and administered the region known as Transnistria where Romanian and German forces killed between 45,000 and 60,000 Jews. By the 16th of September 1943, only 49,927 remained alive out of those who had been deported to Transnistria.
Moldova issued its Declaration of Independence on the 27th of August 1991 declaring the Soviet occupation illegal. This declaration followed the collapse of the Soviet Union which had controlled Bessarabia, Northern Bukovina, and Hertsa until 1991.