They spent a small expeditionary force to secure a fairly large province with high revenue that stayed more or less intact for decades with minimal support?
Because that's all they could afford. Are you saying you expect it to work again and again?
So to wonder whether Christianity would have become the dominant religion in the absence of Islam is to overlook the fact that it already was.
Huh? I don't dispute that the Nestorians
et al. were one of the more important religions of the East, nor that their cultural contributions for the first couple of centuries of the Islamic Empire perhaps outstripped even Muslim contributions, but to say they were
the dominant religion is to overlook the more powerful and centralized church of the Zoroastrians.
And I don't see a reason why political unity of the whole region should be considered a prerequisite for prosperity.
Because that's what generally happens? Not just this example, but numerous other ones: the Romans for the Mediterranean, the various Persian Empires, the Tang for China, Japan when it finally got its act together, the Gupta and Maurya for India... I'm not going to say that political unity is a cure-all for economic and social problems, but it goes a long way towards a more prosperous region. The two are correlated too often to deny that, and its plainly evident to anyone who studies history that when an army goes around ravaging cities and farmland every ten to twenty years, which was the result of the Roman-Sassinid rivalry, then prosperity can never set in.
Uh, let's not idealize their methods. Yes, surely the Arabs were nowhere near as brutal as, say, the Mongols but I wouldn't say that it was particularly rosy either:
The disruption of the existing civilizations must have been huge.
Oh, please. Like any other civilization didn't do this, too. There are numerous examples of Arab conquests where their generals spared citizenry when most other civilizations would have massacred them wholesale. They generally left the dhimmi be, and in many cases when building a new mosque on the site of the old church, would pay the Christians for the land they took. They were a model of tolerance.
As for the economic and social structures of the lands they took, the Arabs left them almost completely intact; Persian and Byzantine organization was only changed in who was at the top of the ladder.
But, without Islam delivering the killing blow, it would have probably stabilized and consolidated.
Why? And even if it did, then why would it
remain stable long enough to conquer the west, and then remain stable even longer to colonize that?
Well, yes. I was reacting to your assertion that without Islam, there would be no trade with the East.
Reduced =/= 0.
For the same reasons Islam expanded into East Africa - trade.
Which, as I have stated above, would be reduced in a region that would still be torn by the violence between Rome and Persia -- not to mention the Arabs who, deprived of Empire, would still be raiding the frontiers.