Romania, officially the Kingdom of Romania (Romanian: România, Regatul României) was a sovereign state in South-East Central Europe. From 1859 to 1877, Romania evolved from a personal union of two vassal principalities (Moldavia and Wallachia) under a single prince to a full-fledged independent kingdom with a Hohenzollern monarchy. In 1918, at the end of World War I, Transylvania, Eastern Moldavia (Bessarabia), and Bukovina united with the Kingdom of Romania, resulting in a "Greater Romania". It bordered the nations of Bulgaria, Hungary, Slovakia, and the Greater German Reich