 To an extent , the Arab – Khazar wars were also linked to the struggle of the Caliphate against the Byzantine Empire along the eastern fringes of Asia Minor , a theatre of war which adjoined the Caucasus . The Byzantine emperors pursued close relations with the Khazars , which amounted to a virtual alliance for most of the period in question , including such exceptional acts as the marriage of emperor Justinian II ( r . 685 – 695 ; 705 – 711 ) to a Khazar princess in 705 . The possibility of the Khazars linking up with the Byzantines through Armenia was a grave threat to the Caliphate , especially given its proximity to the Umayyad metropolitan province of Syria . This did not materialize , and Armenia was left largely quiet , with the Umayyads granting it wide @-@ ranging autonomy and the Byzantines likewise refraining from active campaigning there . Indeed , given the common threat posed by the Khazar raids , the Umayyads found the Armenians ( and the neighbouring Georgians ) willing allies against the Khazars . Although some <unk> , notably Dimitri Obolensky , suggested that the Arab – Khazar wars were motivated by a Muslim desire to outflank the Byzantine defences from the north , this idea is not borne out by the limited nature of the conflict before until the 720s . It is more probable that the Byzantines encouraged the Khazars to attack the Caliphate to relieve the mounting pressure on their own eastern frontier in the early 8th century , as indeed they profited considerably from the diversion of the Muslim armies northwards in the 720s and 730s , resulting in another marriage alliance , between the future emperor Constantine V ( r . 741 – 775 ) and the Khazar princess <unk> in 733 . 
