They fought the Umayyads at their former capital of Balanjar and again under their ruler Barjik, and the leader of these peoples was called a kagan, who was advised by chieftains called begs.
One king of this tribe carried on a correspondence with the Caliph of Cordoba and was named Joseph, who was the son of Aaron II and a member of the Bulanid Dynasty founded by Sabriel. Three tribes rebelled against this group in the Kabar Rebellion, and their last ruler Georgios Tzul ruled a kingdom at Kerch. This tribe had its capital at Atil and maintained the fortress of Sarkel on the Don River. They fought the Umayyads at their former capital of Balanjar and again under their ruler Barjik, and the leader of these peoples was called a kagan, who was advised by chieftains called begs. Byzantine emperor Leo IV was grandson of Bihar, a ruler of this tribe, which gave Leo his epithet, and this tribe was defeated by Sviatoslav I of Kiev and incorporated into the Kievan Rus. For 10 points, identify this tribe, which inhabited central Asia between the seventh and tenth centuries and which notably converted to Judaism.
One king of this tribe carried on a correspondence with the Caliph of Cordoba and was named Joseph, who was the son of Aaron II and a member of the Bulanid Dynasty founded by Sabriel.
Khazars