What went wrong ?

far flung regions adopted the military practices that led to Abbasid success

>>2453798
like what

>>2453777
Qarmatians

The moment they took over Medina, destroyed the Cube and stole the Black stone was the moment every other regional governor smelled blood in the water and the weakness of the Abbasids so they fragmented the Empire from within creating memerates and local dynasties all over the place.

Crypto-Zoroastrians ruin everything.

>>2453777
When you ask "what went wrong" it sounds like you think it could have gone any other way than it did. But what examples do you have of lasting empires that spanned the same space in a similar environment?

Have you considered the possibility that humans simply aren't adapted to such conditions?

>>2453777
The Muslim tax system proved to be ineffective once the general populace started converting, since Muslims paid a lot less tax than infidels.

It was untenable to exert control over such a large area, so various sorts of governors were appointed. Later members of those families were appointed too, and increasingly independent local dynasties started forming.

Turkic slave soldiers and mercenaries became the mainstay of the army and governance system, for a while reducing the Caliphs to mere puppets.

Religious divergence started appearing as a response to unfulfilled social promises and growing tax strain. The Abbasid revolt initially was supported by the peasant army of Abu Muslim, who promised that a more just and equal system of government would be put in place. Later Abu Muslim outlived his usefulness and was murdered - several rebellions broke out in his name in Khorasan, increasingly religiously loaded, often calling him a god. The Shi'a reverted to subterfuge because the Abbasids failed to fulfill their political promises either. There were a lot of other similar groups too, that followed a similar model.