Reddit reviews Muslim Expansion and Byzantine Collapse in North Africa

Responding to your last questions...

On the dwindling of the Arab presence and caliphal authority in the Maghreb, this is a story you see on all of the frontiers of the caliphate. The Arab population was just not large enough to settle the whole of the empire and problems back in Syria and Iraq were constantly drawing more attention.

If you think about the broader conquest of North Africa, the first major campaigns beyond Egypt began in 647, but infighting among the Arabs (which led to the assassination of the Caliph Uthman in 656) slowed progress. The death of Uthman led to the First Fitna, a struggle between Ali (the fourth caliph and first Shi'ite Imam) and Uthman's nephew Muawiya (the fifth caliph and founder of the Umayyad dynasty) that lasted until 661. It wasn't until 665 that Muawiya could organize another invasion of North Africa and that fell apart in 680 when Muawiya died and large parts of the caliphate revolted against Umayyad rule. While the proto-Shi'ite revolt of Hussain (the son of Ali and the third Shi'ite Imam) gets most of the attention, much more serious was the revolt of Abdullah b. al-Zubayr (who declared himself caliph, established a capital in Mecca, and, at one point, controlled Iraq, the Arabian Peninsula, and large portions of Syria and Egypt). This revolt lasted until 692.

So, it's only at the end of the seventh century that the Arabs can make a serious bid for control of North Africa and not until 709 that they can claim full control of modern Morocco, but by 740 the Berbers revolt against Arab rule and end up removing Arab control from everywhere west of Kairouan (roughly modern Tunis). This revolt was fueled by Kharijite teachings that emphasized equality among believers, something the Berbers didn't feel the Arabs were giving them. As this revolt is going on, the Umayyads are weakening and they were probably just happy to hold onto the eastern half of the Maghreb.

Then in 750 you have the Abbasid Revolution and, with that, the total collapse of the Umayyads. The Abbasids never attempted to regain control of any territory west of modern Tunisia for very practical reasons. It was far away, expensive to maintain an army and lines of communication, and they were busy consolidating their own authority in the more central territories. The remains of the Umayyad dynasty found their way to Spain (where the Berber revolts had been successfully defeated) and set up their own state.

This vacuum opened the door for the Idrisids to appear as an Arab Shi'ite dynasty (r. 788-974) (note that the Idrisids aren't originally from the Maghreb, they fled there to escape the Abbasids and used the Awraba Berbers to consolidate power over the other independent Berber states that had developed after the Berber Revolt).
It's not until the rise of the Fatimids in modern Tunisia in the 10th century and their series of attacks on Fes and Sijilmasa that the Idrisids are really challenged by any power from the East.

For further readings, I recommend...

[Walter Kaegi, Muslim Expansion and Byzantine Collapse in North Africa (2010)] (http://www.amazon.com/Muslim-Expansion-Byzantine-Collapse-Africa/dp/0521196779/ref=sr_1_2?ie=UTF8&qid=1376416520&sr=8-2&keywords=walter+kaegi)

Elizabeth Savage, A Gateway to Hell, A Gateway to Paradise: The North African Response to the Arab Conquests (1997)

tl/dr - Morocco was really far away from the center of the early caliphate and it was expensive to send troops, maintain communications, etc. so Morocco developed fairly independent of the rest of the caliphate. Problems back in Iraq, Syria, etc. further made it difficult for the caliphate to put too many resources towards the Maghreb.

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