Okay. But the Mongols were fairly tolerant of other religions as well, I find it unlikely that they would become so zealous as to alter the religious fabric of the areas they rule.
I don't think simply saying Tolerance gives a good summary to the Mongol and even Roman view on religion.
Lots of Muslim writers claimed that the Mongols were attempting to destroy Islam. Their laws against Halal type of animal slaughter were said to be enforced on the pain of death in Chagatai's realm. Clearly and exaggeration but I would say, if the Mongol Empire was structured in such a way where keeping to the Yassa/Law of Genghis Khan and the Shamans was tied to legitimacy, so that they remained pagan for longer they really could have done a number on Islam. Christianity with way less and more flexible rituals would do better but even then, don't expect a switch from this alone as Islam would just be forced to also become flexible on rituals as some "Sufis" already are.
Some very interesting points.
Yes Abbasids were primarily Persian backed, with the bureaucratic elements of the nascent Caliphate, mostly Zoroastrian converts grasping at power. But would they even abandon a prospective chance of greater power to back their closet co-religionists, just for a prospective restoration of Iranian statehood? Where they might even be branded traitors and result in loss of their own life?
Even if a Mazdayan noble might bind these brigands into a cohesive force, he can't do so for long without the support of these administrative classes which in want of more power have abandoned their erstwhile faith. This might just lead to eventual collapse of any such rebellion, even if it can be drawn out for long.
However, those people might back a restorationist rebellion if certain guarantees are made in regards to power sharing arrangements. Though a wholesale defection might not be possible as the opportunities in the enormous Caliphate were simply too good to pass up. And still, the Bavandids of Tabarestan are still no heavyweights to carve out a hefty chunk of Iran, let alone all of it, they simply lack the resources to do so in the span of one rebellion. Remember that their greatest advantage was the Alborz Mountains' defensive terrain. It will be the work of generations for them, but it might just be possible.
Okay, I think these are good points. I guess I just assumed the anarchy at Samara/Iranian intermezzo era were essentially the same as the Fitnahs. What was the difference between both in ur opinion.
My assumption for some Mazyanid would be their own administration gives organization to the whole thing. Given how far Mazyan went OTL and that he was stopped by battle, not logistics or something like that, I would think Tabaristan has the administrative ability.
But anyways, if we go, Umayyads collapse more like the anarchy of Samara and Iranian intermezzo than their actual OTL fall to the Abbasids then we get a majority Zoroastrian population succeeding the Caliphate and already Zoroastrian ruled Tabaristan having more of a chance.
But anyways, the alternative to Mazyanids of Abu Muslim's Zoroastrian supporters successfully revolting. Muslim conversion under the Umayyads and Rashiduns typically involved the convert become a client to some Arab and under the Abbasids this became loyalty to some Muslim figure that the converts heavily associated with. This was Abu Muslim for many and after he died a Zoroastrian general of did Sunbadh, given got an alliance with Tabaristan did revolt but the revolt was crushed in North East modern Iran(Abarshahr).
So, almost my senerio but still wasn't enough. Something that may be enough to flip the balance may be, an immediate revolt rather than Abu Muslim's supporters scattering then revolting at various times from their cores of power. If the Abbasids are too hasty in killing Abu Muslim, he comes to his summons with a larger army or Sunbadh is just better at organizing the smaller force and then the rest of the veterans of Abu Muslim he may be able to unseat the Caliphate and have every ideological and emotional reason to undo Islam.