On March 27, 1918, in the wake of Russia's withdrawal from World War I and its acceptance of the humiliating peace terms set by the Central Powers at Brest-Litovsk, the Balkan republic of Romania annexes Bessarabia, a strategically important area of land located on its eastern border and bounded on the south by the Danube River and the mouth of the Black Sea.
Ruled by Ottoman Turks from the 16th century, Bessarabia (which today corresponds to the republic of Moldova and part of Ukraine) was annexed by the Russians in 1812 as a result of the Russo-Turkish War. The collapse of the Russian empire and the triumph of Bolshevism in 1917 inspired new stirrings of nationalism in Bessarabia, particularly among its large populations of Romanians and Ukrainians.
Despite its historical alliance with the Central Powers, especially Austria-Hungary, Romania had entered World War I on the side of the Allies in August 1916 with the hope of winning Transylvania, then part of Hungary, and expanding its strength in the Balkans. Within six months, however, Austro-German and Bulgarian forces had crushed Romania, effectively overrunning most of the country and ending its participation in the war by early 1917. (It signed a treaty with the Central Powers on May 7, 1918.) With the fall of the Russian empire, however, Romania saw its chance to reestablish its claims over Bessarabia.
For its part, Ukraine saw the end of czarist Russia as an opportunity. Immediately following the overthrow of the czar in February 1917, Ukraine set up a provisional government and proclaimed itself a republic within the structure of a federated Russia. In January 1918, it declared its complete independence. The Ukrainian government immediately sought control of Bessarabia, or at least its northernmost and southernmost sections, where the majority of the population was Ukrainian.
In January 1918, Romania sent troops to Bessarabia; on March 27, after Russia formally exited the war in early March at Brest-Litovsk, it annexed the region. Ukraine's national council strongly protested, urging self-determination for the Ukrainian population of Bessarabia. Over the next year, however, turmoil and ultimately civil war in Ukraine made taking any decisive action impossible. On November 10, a day before the armistice ending World War I was signed—and with an Allied victory assured—Romania reentered the war, occupying Transylvania.
At the Versailles peace conference in 1919, the Romanian delegation, headed by Prime Minister Ion Bratianu, included Bessarabia in a long list of territorial demands that also included the former Austro-Hungarian properties of Transylvania and the Bukovina and Banat regions, all of which they claimed were historically and ethnically Romanian. Though the Supreme Council at Versailles—made up of the leaders of Britain, France, the U.S., Italy and Japan—found Romania's demands excessive, they eventually gave in on most counts, including cession of Bessarabia. Thus, in the post-war period, Romania's size and population nearly doubled, making it by far the greatest winner of territory to come out of World War I.
Neither the new Union of Soviet Socialist Republics (USSR) nor its member republic, Ukraine—which fell to the Bolsheviks in 1919—accepted Romanian control of Bessarabia. During World War II, Bessarabia was occupied by Soviet troops in June 1940, retaken by Romania a year later, and then reoccupied by the Soviets in 1944. After the war ended, the majority of Bessarabia was joined to the soviet republic of Moldavia; the northernmost area and the coastal strip to the south along the Black Sea became part of Ukraine. With the collapse of the Soviet Union in 1991, Moldavia changed its name to Moldova and, along with Ukraine, joined the Commonwealth of Independent States (CIS), an association of 12 former republics of the USSR.