Aborted Islam scenario - How Zoroastrianism fares?

As the title says, take whatever PoD you need after Muhammad's conception and birth that impede Islam from existing at all. This also butterflies away the unification of the Arabic polities. I'm focusing on Persia now, let's leave the Eastern Roman Empire for another debate.

How does Zoroaster's religion fares in this TL? I've read somewhere that it had a much lesser "expansionist" drive in comparison to Christianity, as the religion was wholly associated with the Persian/Iranic identity. Is it correct to say that the Sassanians had no purpose of forcing conversion upon the conquered peoples, such as the Syrians, Judeans, Egyptians, etc.? Could the religion expand more without "official" (state-sponsored) support, for example, among the Central Asian nomads that eventually embraced Islam, or Afghanistan, India, and so forth? What about Arabia itself, will they be more inclined towards Christianity due to the proximity with the Christian Ghassanids and the Lakhmids?
 
Sure it could. Its Gnostic offshoot, Manichaeism was a completely serious contender for replacing paganism before the Pope on one side and the Shah on the other had them all killed. Religion spreads like fire in a forest, slow at first but it gains a steady momentum. There's no reason to assume Zoroastrianism doesn't in a world where most of its followers aren't driven into hiding, exile or worse. As to the specific areas, in the steppe, Manichaeism was mildly popular alongside native Tengriism, India I know less about but it would have to compete with native Hinduism and the other Dharmic religions. In Arabia, I just don't know.
 
I had not forgotten about Manichaeism, indeed they are a very interesting case study on their own right.

Nevertheless, my point concerned more the fact that the Sassanians apparently didn't endeavor to expand Zoroastrianism beyond their own realm. I mean, one thing is a religious tolerance policy, as some Shahs tolerated Christians and Jews, but on the other hand could the official Ahura Mazda's cult reach the same level of influence that Islam attained in the Near East, competing with eastern Christianity?
 
I could see it being the most popular religion in Iran definitely, and if it can get some reformation that makes it more....convert friendly (less conservative and powerful clergy, remove connotations of Persian ethnic supremacy) then it could also definitely take Afghanistan, parts of the Subcontinent, Central Asia, etc. Maybe if you have a warlike steppe people adopt it you can see it spread as far as Russia, Mongolia and perhaps even make some headway in China.
 
I could see it being the most popular religion in Iran definitely, and if it can get some reformation that makes it more....convert friendly (less conservative and powerful clergy, remove connotations of Persian ethnic supremacy) then it could also definitely take Afghanistan, parts of the Subcontinent, Central Asia, etc. Maybe if you have a warlike steppe people adopt it you can see it spread as far as Russia, Mongolia and perhaps even make some headway in China.

I think that a stronger Mazdakian movement might be able to bring about some of these changes. The problem, of course, is that Orthodox Zoroastrianism was so closely tied to the Sassanid dynasty that it would be difficult to see a serious effort to undermine the faith by a member of that dynasty. What you might need is a period of chaos following that collapse of the Sassanid Dynasty and a new dynasty coming to power to really get some substantial reformation of Zoroastrianism. Also, having the faith less tied directly to the dynasty might help encourage them to look outside of Persia's borders for converts.
 
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