Part III (= Chapters 7 and 8) of MacCulloch's survey of Christian history takes up the story of the early church in the south and east after the Council at Chalcedon (451). These movements were partly the result of a debate about the nature of Christ.
The formula from Chalcedon said that Jesus Christ was "one person in two natures," human and divine. Most everyone agreed that the reported claim of Nestorius--that within Christ there were two persons--was absolute heresy. But for believers in places like Alexandria, it was also wrong to speak, as Chalcedon did, of Christ having two natures. The detractors explained that as wine and water become indistinguishable when mixed, so the human and divine in Christ were indistinguishable and essentially one. This was the position of the Monophysite movement. (MacCulloch calls this "Miaphysite." Both terms mean "one nature").
With their center of influence at Alexandria, the Miaphysites dominated northeast Africa. From there and also from the east bank of the Red Sea, the faith traveled further south into Africa all the way to Ethiopia. As a way of expressing their differences with Chalcedon, African Christians adopted the language called Coptic. On occasion, leaders at Constantinople attempted to strike a deal, holding to the Chalcedonian creed while maintaining ties with the Miaphysites. These efforts ultimately failed until, eventually, the southern churches became so institutionally and culturally different from Constantinople and Rome that the two sides were practically irreconcilable.
Another group breaking with Chalcedon went in the opposite theological direction and in a different physical direction. The Dyophysites emphasized the separateness of the human and divine in Jesus. Thus the early church's christological debate provided three distinct options: Miaphysite (one nature), Roman/Chalcedonian (two natures in one person), and Dyophysite (the human nature of Christ is separable from his divine person). The Dyophysite movement took root, often as a distinct minority, in various parts of Asia traveling as far east as India, China, and even Japan.
In chapter 8, MacCulloch shows that the rise and conquests of Islam and/or the presence of indigenous religious traditions had the effect of cutting off Africa and most of Asia from Roman and Byzantine expressions of Christianity. Those believers isolated in the South and East were often persecuted and oppressed. Nevertheless, they held to their faith (regarded by the West as heretical). The result is that there are to this day many vestiges of Christianity in Africa and Asia. And MacCulloch is convinced that a large number of these have yet to be appreciated or discovered by the West. He remarks that in the centuries following the break up of these two Christian worlds, what is truly remarkable is
just how little Western Chalcedonian Christians knew about centuries of Christian struggle, scholarship, sanctity and heroism in another world. Western Christianity, heir to Chalcedon, Reformation and Counter Reformation, still has a long way to go before the balance is fully righted.
Western Christians have forgotten that before the coming of Islam utterly transformed the situation in the eastern Mediterranean and Asia, there was a good chance that the centre of gravity of Christian faith might have moved east to Iraq rather than west to Rome. Instead, the ancient Christianity of the East was nearly everywhere faced with a destiny of contraction in numbers, suffering and martyrdom which still continues (284).
To this point in the book, I think this is the most impressive and important section.