I stated earlier that, yes, there probably was a historical Mohammed
who was a king
and who considered himself some kind of prophet.
The point I was making is
that the Mohammed of the Koran and the Hadith is a mythological person
who bears very little resemblance to any historical person.
Further more, the 'theology' of Islam
(such as it is)
probably originated in Syria not in Mecca and Medina.
"a single man organized a new state centered on Medina and from it conquered Mecca, and imposed a monotheism on the pagans of Arabia"
and said that this account - "is not disputed by any serious historian."
You replied with statements claiming nothing is actually known from contemporary documents of Muhammad, and added -
"Islam probably did not originate in Medina and Mecca but in Syria"
Which I consider to be historically false, as a matter of the well known political history, as I thought I made quite clear. You gave as a rationale (with the proviso that you are not an historian) that Syria -
"was far more advanced culturally and had much greater contact with Judaic and Christian ideas."
Thus implying, in effect, that it was implausible that anyone named Muhammad off in the Hijaz had actually come up with anything so scriptual and revelationee, and it must have actually been founded by Christian ideas in Syria.
The reason this is historical nonsense is easy enough to state. There wouldn't have been a new dynasty with a new doctrine in Syria if there hadn't already been an organized and successful military and religious movement riding out of Arabia under Omar. Syria did not invent Islam and backdate its origins to the Hijaz a century prior.
Syria was a Byzantine province, governed from Antioch while answering to Constantinople, speaking Greek, and practicing Christianity not Islam. Then a bunch of Arabs rode in under this Omar dude and beat the hell out of them, imposed taxes on them, and settled down to rule the place. They were already monotheists - they had imposed monotheism on the whole Arabian penisula already. Christian Syria would not have changed its doctrine at all, absent the political, military, and religious movement known as "Islam". Which therefore already existed (! - I thought that part was obvious).
Now, you can say in matters of doctrinal detail, there were Christian influences stemming from Syria, certainly. Also from Egypt, when Alexandria was taken e.g. There were later ones stemming from Zorastrians in Persia, and under the Abassids from court ordered translations of greek philosophy, Indian religious texts, Sabean astrology, yada yada. Jews had influenced the movement even back in its days in Medina, according to Muslim report anyway (we have little outside info).
In other words, I saw you are too easily conflating the time the Koran was written down with the origin of Islam, and insinuating from that that Islam is basically a Syrian Christian innovation. Which struck me as wildly implausible, and as putting a little theological detail caboose way in front of a giant military-political "whole point" engine.
The basic doctrine they were fighting for (simplified monotheism, aka "Arianism squared" if you like) was set long before they got to Syria, and for good or ill created the political unity that, along with Omar's military leadership, made that conquest happen.
It is, incidentally, rather easy to see why that particular doctrine was attractive to any ambitious potentate in Arabia. Arabia was neutral ground between the contending great powers, exhausted at the time but financially and culturally much larger powers, Parthian Persia and Greek Byzantium.
The doctrine of the Parthians was a dualist derivative of Zorastrianism, meaning big cosmic fight between the good creator God and the evil devil, everyone choose a side, and a big day of judgment. The doctrine of Byzantium was Christianity, which was just getting through the Arian heresy period - which had been particularly popular in the army. The Arian heresy, of course, was denial of the full divinity of Christ, aka a tendency to reduce Jesus almost to just a wise teacher, by over-emphasizing the absolute transcendence of God the Father.
Split the difference with a "syncretic" compromise, dropping elements only found in one but not found in the other. Big cosmic fight, absolute God the Father, only a teacher - prophet not an incarnation, day of judgment. Drop all the complications and subtle aspects of either teaching.
It was a stripped down syncretic compromise, meant to be freed from accretions of this and that, and meant to eliminate anything distinctively the property of only one of the two. It was meant to appeal to Arians within Byzantium and ethical monotheists within Parthia, on the basis of simplicity. Thus to the soldiers, rather than to priests of either.
So there is no great mystery about where the basic content of the doctrine comes from. As for filling in details about predestination this or free will that, God's knowledge of this and grace about that, sure that all probably came from Syrian theologians, skewed by which doctrines seemed useful to the Umayyads or fit the temperment of Arab soldiers, etc. But that is details.