[1] Before the Muslim conquest in 638–640, there were long-established nomadic and semi-nomadic Arab tribes in the desert fringes of the upper and lower Euphrates valley and, to a lesser degree, nearer to the settlements along the river banks.

[5] These lands were occupied by the nomadic components of the Muslim armies, mainly from the Qays tribes, over whom the commanders appointed by Medina had little to no control, and who paid the minimal tithes to the caliphs.

[5] The Muslim tribesmen played a key military role in defending the eastern flank of Syria from Byzantine incursions, and benefited from the lucrative raids into Armenia.

[8] Upon the caliph's instructions, Mu'awiya ibn Abi Sufyan, who governed the region, settled Arab tribesmen on unclaimed or vacant lands in the Jazira, some distance away from the settlements along the Euphrates, and gave them permission to engage in agriculture.

[9] Likely to assuage the concerns of the earlier-established Qays tribesmen, the newer arrivals were excluded from military service on the Armenian frontier and were placed in strategically located points, such as intersections of major routes or narrow mountain passes, to act as a buffer against Byzantine assaults.

[15] Iyad ibn Ghanm frequently besieged walled settlements along the Euphrates and Khabur rivers before or during harvest time, while sending detachments of troops to raid the surrounding countryside for agricultural supplies and captives among the peasantry.

Iyad ibn Ghanm's objective was to capture cities with minimal destruction, so as to ensure the flow of tax revenue, as well as agricultural goods, to the conquerors.

[23] Nonetheless, the composition of the Arab tribes in the Jazira in the post-conquest period, characterized by the predominance of the Mudar group (e.g. Qays, Asad, Tamim), made it "a somewhat separate entity", according to the historian Khalid Yahya Blankinship.

[23] Although the original Qaysi conquerors tolerated the flow of immigrants during Mu'awiya's lifetime, they resented that their territory was singled out for the resettlement of outside tribesmen, rather than Syria proper where the tribes who later constituted the Yaman faction and were closely allied to the Umayyads held sway.

[24] During the Second Muslim Civil War, the Qays tribes of the Jazira backed the Mecca-based opponent of the Syria-based Umayyads, Abd Allah ibn al-Zubayr.

A leader of the Qays, Zufar ibn al-Harith al-Kilabi, afterward rallied the tribe's opposition to the Umayyads from the fortified Jaziran town of Qarqisiya (Circesium), located near the confluence of the Euphrates and Khabur rivers.

[32] After a number of Umayyad sieges against Qarqisiya, Zufar surrendered to Caliph Abd al-Malik (r. 685–705) in 691, abandoning Ibn al-Zubayr's cause and obtaining military and courtly privileges for himself and his sons.

[23] According to the historian Hugh N. Kennedy, it was done at the request of Muhammad ibn Marwan, Abd al-Malik's brother, and thenceforth the tribal troops of the province "lived off its revenues".

[22] Mosul became a dependency of the Jazira in 721–725, a period in which the Jaziran troops had attained prominence among the Umayyad armies for their suppression of the major rebellion of Yazid ibn al-Muhallab in Iraq in 720.

More politically and militarily significant than Mosul were the northern frontier regions of Arminiya and Adharbayjan, which were attached to Muhammad ibn Marwan's Jaziran governorship in 702.

[37] Although the Jazirans were largely able to suppress the renewed dissensions against the Umayyads in Iraq, the main challenge to the dynasty emanated from the far eastern frontier province of Khurasan.

In the words of Kennedy, there ensued what "can be seen as the struggle of one frontier army, Marwān's men from the Jazīra and the Caucasus [Adharbayjan and Arminiya], against another, the pro-Abbasid troops from Khurāsān.