Khazaria long served as a buffer state between the Byzantine Empire and both the nomads of the northern steppes and the Umayyad Caliphate and Abbasid Caliphate, after serving as the Byzantine Empire’s proxy against the Sasanian Empire. The alliance was dropped around 900. Byzantium began to encourage the Alans to attack Khazaria and to weaken its hold on Crimea and the Caucasus and sought to obtain an entente with the rising Rus’ power to the north, which it aspired to convert to Christianity.