What would a Christian Arabia actually be like?

Arabia would not extend past the Syrian Desert. The Levant, Mesopotamia and Egypt would not bee... Arabic...

I'm not entirely convinced of this. Arabia didn't need Islam to unify. It helped, sure - but you already had Arab migrations into Mesopotamia at Al-Hira, the Annizah, Nabateans, etc. The region wasn't particulary stable on the Roman or Persian side.

Just to look at the Persians, where the most opportunity lies, lets get back to Al-Hira. Still protected by the Lakhmids who'd been punished by the Persians a couple of decades earlier. With the instability following the execution of Khosrau II. This actually leaves the Lakhmids in an interesting position, they could both avenge their previous punishment, and become very powerful if they basically open their doors to their fellow Arabs, especially Arab Christians and even local Christians. You could see the rise of a Christian Arab Mesopotamia quite easily. Even if it isn't independent, it could rapidly establish itself as a power-broker in Persian politics.

As with Syria and Egypt - the Romans can always use soldiers. Migration, settlement, recruitment, repeat - assuming they live on the border fringes, you could still see the region Arabise, especially if the Roman Empire falls apart ITTL. Regardless, they can become a significant demographic within those regions.
 
Arabia would not extend past the Syrian Desert. The Levant, Mesopotamia and Egypt would not bee... Arabic...

I'm not sure that's 100% true because the languages of the Levant were related to Arabic. The Aramaic for example.

My wife speaks Arabic and when I read to her the last words of Jesus, written in the original language, she understood what he was saying and translated it for me.
 
eionite.png
A map of the Ebionite dicoeses in Arabia. Darker color is for archdioceses.

Okay lets be more serious: By Arabia we consider Jordan, Saudi Arabia, Gulf countries , Oman and Yemen.
Jordan , at least the more humid parts would remain Orthodox under th ePatriarchate of Jerusalem. The desert areas, as well as places like Maan and Aqaba might become home to religious dissidents fleeing from Byzantien inquisition. Given the cultural context, most of the them would be Jewish Christians, that is something like Ebionites and Nazarenes. This religious branch would spread into Hejaz, which would have also Jewish population. (Mohammed met a Jewish tribe in Medina). My bet is, that eventually either Ebionites or Jews would come to dominate the region. T
The Gulf countries : Qatar, Bahrain, UAE, Kuwait and Saudi Arabias Eastern Province would go Nestorian. Proof: existence of Bishops of Beth Qatriye and Mazun, as well as Jubail Church in Saudi Arabia. oman is a tricky one. Dependent on who gets there first, it could be either Nestorian, Hindu, Zoroastrian or even Jain.
Yemen can also choose from a variety of possibilities. it can go Miaphysite (from Ethiopia), Nestorian, or Jewish. Judaism used to have a strong presence over there.
Najd seems to be a place for some rather strict religious movement : the ebionites would serve it well, while some Phariseeic interpretation of Judaism is not out of question either.
 
So to tie all that back to my original point: even in a "no Islam" situation, a lot of the features which outsiders mistakenly attribute as "Islamic" would still exist anyway, even in a Christian format, because they are deeply ingrained in the culture for thousands of years.

Though I dislike the religion (not the people though), there would be many similarities between an Arabian Christianity and Islam as the latter is heavily influenced by Arab paganism. Just take the Kaaba as an example.

But I will like to raise a question. The early history of Islam is very blurry and actually suggests that it was possibly created during the start of the Umayyads in order to unite the populations. There is even evidence to suggest that Mohammad was a composite figure. This isn't the mainstream accepted opinion but how would Arabia play out if this was the case and no Islam arose?
 
Though I dislike the religion (not the people though), there would be many similarities between an Arabian Christianity and Islam as the latter is heavily influenced by Arab paganism. Just take the Kaaba as an example.

But I will like to raise a question. The early history of Islam is very blurry and actually suggests that it was possibly created during the start of the Umayyads in order to unite the populations. There is even evidence to suggest that Mohammad was a composite figure. This isn't the mainstream accepted opinion but how would Arabia play out if this was the case and no Islam arose?

Does this relate to Tom Holland's conspiracy theory version of Islamic origins?

I saw a tv program about that. It was up there with Ancient Aliens in terms of credibility. He kept repeating "but there's no evidence" over and over, and then comes up with this bizarre theory that makes no sense whatsoever and goes completely against all established facts.

One wonders whether he really believes any of it, or whether he is simply trolling to get ratings.
 
A couple of thoughts. The Persian influence on the Arabian side of the Gulf and parts of OTL Iraq would remain strong, and absent the physical conquest of Persia would Christianity replace Zoroastrianism in Persia and Persian influenced areas, or gain some place as a minority religion. While some customs we consider "Islamic" may be more modern, certain parts of Arab Islamic culture derive from tribal/Arab customs of the pre-Muslim era. Just as some of these were absorbed in to Islam, how many of these would be absorbed in to "Arab Christianity". Would multiple marriage still be acceptable? (1) Also, there was a good deal of preservation of pre-Christian learning as well as new thinking that came from the Islamic world 800-1500 AD. Would some of this old learning be destroyed as "pagan" like it was in the west, would algebra and other new techniques come forward as soon (and what about Arabic numerals...).

(1) Following the 30 Years Wars in the Germanies, having two wives was briefly allowed due to the loss of so many males.
 
Does this relate to Tom Holland's conspiracy theory version of Islamic origins?

I saw a tv program about that. It was up there with Ancient Aliens in terms of credibility. He kept repeating "but there's no evidence" over and over, and then comes up with this bizarre theory that makes no sense whatsoever and goes completely against all established facts.

One wonders whether he really believes any of it, or whether he is simply trolling to get ratings.
It wasn't from Tom Holland but when you look at the early history, it is weird.

Firstly, the mosques built in the first 100 years had their qibla point to Petra whilst the following 100 years had them pointing wherever and only after 200 years did they all start pointing to Mecca.
Secondly, Muslims believe that Mohammed lived in Mecca but the description of where Mohammed comes from doesn't fit Mecca but it does fit Petra. There is also the fact that the first Qurans were written down during the reign of the Rashidun Caliphs and has been changed many times over the span of history so that discredits the Islamic claim that the Quran is unchanged.

In conclusion, I believe that there was some sort of semi-religious movement in Arabia and that Mohammad is a composite of at least two figures with one coming from northern Hedjaz and one coming from southern/central Hedjaz. Once the Arabs began consolidating their gains, they began the creation of what would become Islam and thus took bits and pieces from all sorts of religions. For example, in Islam there is a belief that you will cross a bridge over hell. Zoroastrianism also has this belief.
 
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