How can Iran become a majority-Christian nation at any point before or after the rise of Islam? What would the ramifications of such a state be?
That would butterfly out of control.Some form of Miaphysite/Oriental Orthodox Church could have been seen as distinct enough from the Roman/Greek variety that the Persians may have been more eager to adopt. You could also take Armenian missionaries and have them spread Christianity and convert the empire. Or one could change Muhammad's vision from God and have it so that he interprets it as a call to convert the Arabs to Christianity and subsequently spread east to complete an Arab Christian conquest of Persia.
How can Iran become a majority-Christian nation at any point before or after the rise of Islam? What would the ramifications of such a state be?
After Islam it is out of question to turn ChristiN. It either remains Islamic, or Zoriastrian as they are likely to turn hostile to outside powers experiencing the threat. Depending on the time. And the East Romans are in no position to conquer Persia assuming Arab armies conquer Levant and Egypt anyway.
Before Islam it depends on some factors:
- did the East Roman Empire turn West yet?
- how strong is Persia?
If Persia is as weak as post-war but the Roman Empire being still strong, it has to conquer Persia to turn it Christian. Islam grew with 200 years of Arab Rule and later Islamic Persian rulers. Odds are the same the very same can happen in a Christian scenario. Roms does not have to permanently rule Persia. Just long enough to make it turn the ruling elite Christian. The natives will do the rest.
Another option is for the Göktürks to convert to Christianity and let them conquer Persia. Afterwards, the same route like the East Romans can be followed.
Nestorianism can possibly gain traction in Iran simply because the Ephesian Schism left it disconnected from Rome. If Iran becomes Nestorian in the fifth or sixth century, this has a major impact on the dynamic between Constantinople and Ctesiphon. Wars of religion between the two empires would be over who had the right brand of Christianity. The butterflies are potentially enormous.
I would opine that a Christian Persia just means any ATL Arabic invasion leads to the conversion of the Arabs to Christianity.
Why? The Arab conquests were to some degree very much only possible thanks to the unifying message of Islam.
There's considerable thought around here - at least from folks I've seen - that Islam or no Islam, an Arabic demographic explosion outward was inevitable. I would add that Islam worked especially in the religious diverse/contentious lands they conquered. If they're all Christian, it would make sense for them to adopt Christianity, no? That's how it worked with basically every other nomadic conquest
I'm kinda flying blind here as I don't know a ton about the era but isn't a possible POD to have Muhammad be a Christian and conquer Persia like OTL only as a Christian?
Some form of Miaphysite/Oriental Orthodox Church could have been seen as distinct enough from the Roman/Greek variety that the Persians may have been more eager to adopt. You could also take Armenian missionaries and have them spread Christianity and convert the empire. Or one could change Muhammad's vision from God and have it so that he interprets it as a call to convert the Arabs to Christianity and subsequently spread east to complete an Arab Christian conquest of Persia.