Moreover, the Monophysites of those provinces were happier (at that time) under Muslim rule than they had been under Orthodox rule.Well, of course. I learned that in grammar school.
I thought you were being serious before. Now, I suspect there might've been a touch of sarcasm... LOL
Well, what I was getting at is this: Egyptians in the 7th century mostly adhered to a Monophysite Christology that held Christ to have only one nature (mono = one and physi = nature, in Greek). This was opposed to the Orthodox Chalcedonian position that Christ is both fully human and fully divine. The Egyptians were inclined toward Eutychian version of Monophysitism, which held that Christ's human element, if he had any, was completed submerged by his divinity ("dissolved like a drop of honey in the sea").
By contrast, many Syrians were Nestorian, which for some enigmatic reason I don't fully understand is oftentimes confused with Monophysitism (although there were also many Syrian Monophysites, but those tended to be Apollinarians or Monothelites, which basically held that although Christ had indeed been human his mind was in full divine union with God's). Anyhow, Nestorians believed that Jesus Christ was two distinct, separate entities: One human and the other divine, so it was indeed the opposite of Monophysitism (which is why the confusion is inexplicable to me).
Nestorianism was basically Neo-Adoptionism, which is the idea that Jesus was a regular man who was so holy as to be adopted by the divine Christ as his emissary. Adoptionism was a view held by many Jewish-Christians before they faded with the rise of rabbinic Judaism. Jewish-Christian ideas were very influential in Antiochene theology and evidently spawned Nestorius' creed.
In any case, both Monophysite and Nestorian Christologies were regarded as the worse type of heresy by the Orthodox overlords, who mistreated the natives accordingly. When they found that the Muslims were (initially) much more tolerant of heterodox Christian views (obviously, since the Muslims didn't care which version of Christianity their Christian subjects followed) they were not at all inclined to return to the persecution of the Orthodox Byzantines.
One thing that the Muslims did achieve was to sweep away much of the variety in Christian thought, since most all of the opposition to what became Orthodoxy and Catholicism was centered in the regions that the Muslims conquered. Things were relatively orderly after that until Martin Luther came along, not counting the whole Albigensian unpleasantry (and they were more Manichaean than Christian).
1) Chalcedonians are termed after the Council of Chalcedon that was convened in 451 to condemn the Monophysite heresy. It basically reaffirmed the paradoxical non sequiturs of the unitary dual nature of Christ and of tritheist monotheism that have become orthodox Christianity (which includes both Roman Catholicism and Eastern Orthodoxy).
2) Manichaeism was a dualist religious creed perhaps best described as falling in that class of religions (such as Daoism and Zoroastrianism) that view the divine realm as equally balanced between the force of good and the force of evil (though they arrive at this by varying rationales). The founder, Mani, regarded himself as a Christian, but Manichaeism is so far removed from the what became the 'mainstream' of Christian theology that it is almost always referred to as if it's a separate religion, rather than a Christian heresy. That may be accurate, since it was essentially a synthesis of Christian, Persian, and Buddhist concepts.
3) A key distinction of Manichaeans is that most of them embraced the concept of the phenomenal world (Earth and humanity) as an evil realm. This was a very Gnostic concept, although Christians in general tend to agree, just more ambivalently. It's also a very Buddhist concept, and perhaps foremost a Buddhist concept because some scholars argue that Basilides and Valentinus (who were the founders of the most 'recognizably Gnostic' creeds) were influenced by Buddhist thought. However, it's worth noting that Manichaeism is thought to have more in common with Marcionism than with Valentinism. Marcion's heresy was the (very reasonable) notion that the Old Testament god was vindictively evil and obviously different than the benevolently good God described by Christ. Anyhow, the most extreme Manichaeans even considered childbirth (and procreative sex) evil because it perpetuated the alleged evil of the material realm.
4) The great opponent of the Manichees was St Augustine, who had himself been a Manichee hedonist in his youth, but conveniently saw the light once he had his fill of debauchery (see The City of God). After St. Augustine, Manichaean were revived amongst the Paulicians of Anatolia and the Priscillianists of Iberia. Priscillian was basically a hard-core mystical ascetic (for which he became the first of many, many Christians to be executed for heresy). By contrast, the Paulicians rejected the Church hierarchy and the orthopraxy of Christian conduct.
Historically, the very same two responses always emerge from any creed (such as Gnosticism, Buddhism, or Manichaeism) that regards the phenomenal world as evil: (a) the encratite response holds that salvation is to be found by strict asceticism; that since the world and human nature is evil, one must refrain from behaving human; (b) the antinomian response holds that since the phenomenal world (and especially the human body) is evil, that it doesn't matter what one does with one's body, because only the soul matters. Oftentimes, the idea is that sensory experiences of whatever kind aid the soul in achieving enlightenment and transcendence.
They are just two extremes of the weird tendency of humanity to abhor and debase itself.
5) Getting back to the point, the Albigensian Catharists of Aquitaine Spain were the heirs of the Priscillian heresy, and therefore indirectly Manichaean (and therefore indirectly Marcionite). As for the Paulician heresy, its last gasp was amongst the Bogomil heresy of the Slavs (which to be exact was a synthesis of Armenian and Slavonic gnosticism). In any event, the core tenet of the Albigensian creed was that the material world is evil, created by the "demiurge" god of the Old Testament ("demiurge" means the 'fashioner' or 'designer' of the universe, since only an evil, fallen god would fashion such an evil, fallen realm). Albigensians believed in reincarnation and that the way to escape the cycle of rebirth was by absolute asceticism, which is why they were called Catharists (which means 'cleansers'). Although, bear in mind that their moral system was upside down by more familiar standards (they had less of a problem with homosex, by example, since it did not result in childbirth, than with procreative sex, especially nonmarital fornication).
So, to explain my comment before, the Albigensians were branded as evil heretics and (since they were also very wealthy) Pope Innocent III invoked a Crusade and then an Inquisition against them in the 13th century and they were obliterated.
I hope that helps clear things up!
What crossover beliefs are there with Buddhist?