The underlying issue in the Republic of Moldova revolves around ethnicity and whether the country should re-unite with Romania, with which it shares a common ethnicity, language, culture and history. The Republic of Moldova represents roughly the eastern half of what is historically known as the Principality of Moldova. As a result of the Treaty of Bucharest (1812), ending the Russo-Turkish War of 1806, it was separated from the western part of the principality along the Prut river and annexed by the Russian Empire, which named it Bessarabia (Basarabia). The western half of the former Principality of Moldova, which was not annexed by Russia, united with Wallachia (Țara Românească) in 1859 to form the basis for modern day Romania. The eastern half united with Romania in 1918, but was re-annexed by the Soviet Union in 1940 as a result of the Molotov-Ribbentrop Pact.