So I was reading the
what if Pilate spared Jesus thread, and thought instead what if Islam took root in the Roman Empire? Say, for example, the extent of Roman conquests in the Middle East is more comprehensive in TTL, leading to the annexation of the whole, or at least majority, of the Arabian Peninsula including Medina and Mecca. Then, I can see two ways to this.
1. Jesus is not born in TTL or any other similar Messiah. So say things continue to move along except with a few butterflies, i.e. Constantine doesn't become Christian. Then when Islam comes around, Constantinople is hard-pressed to accept it just as Christianity was in OTL. So what effects would this have, both short and long term, considering that the extent of the spread of Christianity would have been limited only to the Eastern Roman Empire?
2. Jesus dies as per OTL, or in any other way for that matter. But say Islam comes around much earlier, say around the time of Jesus. Or even vice-versa, Jesus being born around the time of OTL's birth of Islam (Though I must ask if this sounds ASB? Personally I should think not, thinking in purely secular terms, I think it's possible that events like these could have happened at different times, though admittedly with major butterflies). What would happen? Would there be a competition between both? Would the Roman State tolerate both, even adopt both religions? Maybe even combining both Abrahamic religions, though I don't know if this is possible. Short and long term effects, politically, culturally, etc?