To add to this, the single country with the most Catholics is India. Jesus disappeared for 18 years. The philosophy that he espoused on his return is remarkedly like Hindu. The Trinity, turning the other cheek. That coupled with the Horus legend made up the rest. Just my 2 cents.

It is the nature of religion, because of the lack of independently-verifiable evidence for many of its assertions, to undergo schism. Both Christianity and Islam are products of schism, having split off from Judaism. All three of these have split repeatedly, Christi-insanity alone having produced some forty thousand sects. So if it had not been Islam, it would have been something else.

It is/was my understanding that in Islam Jesus is another prophet, an important one, but no more than a prophet. Is that incorrect?

As a historian I was taught that the less useful questions are the -what if- ones... What matters is what happened and why it happened.

The Qur'an originally developed as Muhammad's attempt to make the Hebrew (and some Christian) sacred texts available in Arabic to the Arabians. After converting some Arabians to Islam, and being rejected by the Jews Christians and "pantheists", "the prophet" ceased being a missionary and became a warlord. Since then, Islam has been successfully spread by warfare (Jihad). I doubt that the dogma of the Trinity was a factor.

I believe Islam was a forced conversion by Mohammed, basically was convert or die.

Islam didn't start as a religion for about another thousand years. I am more inclinded to believe it was developed more as an antithesis to the Christian religion being shoved into the Eastern Roman empire from the Western Roman empire .... Kind of a "no we don't need your BS, we have our own".

I reckon the Trinity probably helped Islam to appeal to a lot of people who rejected Christianity for being too theologically weird.

Which rings me to my next question, how widespread was knowledge of these kind of details of the faith? Possession of ancient bibles in Greek or Latin must have been limited to the clergy no? And relatively few people could read or write.

Interesting idea. I don't know enough about history to comment further.

who knows constantine seemed to be using it to solidify his power the islamic nations at the time were very forward thinking and scientific but as with all things religion doesnt like sharing power i think we can all agree without its influence our lives now would be way more amazing (im talking flying cars and hols on the moon amazing wheres my flying car religion???)

We can't know either way. For all we know the Trinity was what kept Christianity together and without it it would have crumbled. Maybe, maybe not. Some things are too complex and there's too little information make any definite claims.

The rise and fall of religions has many variables. Any one thing can only have a limited effect.

Would Islam have died if the trinity was not a thing? Probably not.

Would it have been hindered? Probably so.

I like the thought process you are using.