Principality of Serbia or Serbian Principality (Serbian: Cрпска Кнежевина) or Rascia (Serbian: Рашка) was an early medieval state of the Serbs ruled by the Vlastimirović dynasty, that existed from ca 768 to 969 in Southeastern Europe. It was established through an unification of several provincial chiefs under the supreme rule of a certain Višeslav, the first known Serbian ruler by name ( 768–814). In 822, the Serbs were said to rule the "greater part of Dalmatia", and at the same time the Bulgars had taken the lands to the east, preparing to conquer Serbia. Vlastimir of Serbia defeated the Bulgar army in a three-year-war (839–842), and the two powers lived in peace for some decades. Vlastimir's three sons succeeded in ruling Serbia together, although not for long; Serbia became a key part in the power struggle between the Byzantines and Bulgars (in predominantly Byzantine alliance), which also resulted in major dynastic civil wars for a period of three decades. Serbia was annexed by the Bulgars for three years (924–927), until the return of the political hostage Prince Časlav, who united several provinces, becoming the most powerful of the Vlastimirović. An important event was the establishment of Christianity as state-religion in 869 AD, and the founding of the first Serbian eparchy, the Eparchy of Ras. The information of the Vlastimirović dynasty ends with De Administrando Imperio (fl. 950–960). Serbia is annexed by the Byzantines in 969.