Bessarabia is a historical region in Eastern Europe, bounded by the Dniester River to the east and the Prut River to the west. 65% of Bessarabia covers Moldavia, with the Ukrainian Budjak region and part of Chernivtsi Oblast covering a small area in the north. In the aftermath of the Russo-Turkish War of 1806-1812, the Ottoman Empire ceded Bessarabia to the Russian Empire, one of the empire's last territorial acquisitions in Europe. Following the Crimean War in 1856, southern Bessarabia was returned to Moldavia, only for Russia to regain the entirety of the region in 1878 after Romania, which had conquered the region from the Ottomans during the Russo-Turkish War of 1877-1878, exchanged Bessarabia for the Dobruja. In 1917, in the wake of the Russian Revolution, a Moldavian Democratic Republic was created. In 1918, the Romanian Army was sent to pacify the region, and the parliamentary assembly declared a union between Moldavia and Romania. In 1940, the Soviet Union reclaimed Bessarabia after threatening Romania with war, with Nazi Germany providing the USSR with tacit support as a result of the Molotov-Ribbentrop Pact. The area was formally integrated into the USSR as the Moldavian ASSR, later becoming the Moldavian SSR. In 1941, Romania recaptured the region during Operation Barbarossa, but lost it in 1944 as the tide of the war changed. Moldavia remained a part of the USSR until 1991, when it gained independence as "Moldova", while Transnistria split off from Moldova to protect the rights of ethnic Russians in the country. Today, the majority of the region is controlled by Moldova, with the rest being controlled by Ukraine.