Bessarabia (ˌbɛsəˈreɪbiə; Besarabiya; Basarabia; Bessarabiia) is a historical region in Eastern Europe, bounded by the Dniester river on the east and the Prut river on the west. About two thirds of Bessarabia lies within modern-day Moldova, with the Ukrainian Budjak region covering the southern coastal region and part of the Ukrainian Chernivtsi Oblast covering a small area in the north.
In the aftermath of the Russo-Turkish War (1806–1812), and the ensuing Peace of Bucharest, the eastern parts of the Principality of Moldavia, an Ottoman vassal, along with some areas formerly under direct Ottoman rule, were ceded to Imperial Russia. The acquisition was among the Russian Empire's last territorial acquisitions in Europe. The newly acquired territories were organised as the Bessarabia Governorate of the Russian Empire, adopting a name previously used for the southern plains between the Dniester and the Danube rivers. Following the Crimean War, in 1856, the southern areas of Bessarabia were returned to Moldavian rule; Russian rule was restored over the whole of the region in 1878, when Romania, the result of Moldavia's union with Wallachia, was pressured into exchanging those territories for the Dobruja.
In 1917, in the wake of the Russian Revolution, the area constituted itself as the Moldavian Democratic Republic, an autonomous republic part of a proposed federative Russian state. Bolshevik agitation in late 1917 and early 1918 resulted in the intervention of the Romanian Army, ostensibly to pacify the region. Soon after, the parliamentary assembly declared independence, and then union with the Kingdom of Romania. However, the legality of these acts was disputed, most prominently by the Soviet Union, which regarded the area as a territory occupied by Romania.
In 1940, after securing the assent of Nazi Germany through the Molotov–Ribbentrop Pact, the Soviet Union pressured Romania, under threat of war, into withdrawing from Bessarabia, allowing the Red Army to enter and the Soviet Union to annex the region.