Viisaus asked me about this, and I told him I'd get back to him on it.
According to Samuel Hugh Moffett, in his work "A History of Christianity in Asia, Volume 1" (Maryknoll, NY: Orbis Books 1997) the schism that happened at the time of Ephesus and Chalcedon caused splits very much akin to what happened in Europe during the Reformation. He describes it:
What finally divided the early church, East from West, Asia from Europe, was neither war nor persecution, but the blight of a violent theological controversy, that raged through the Mediterranean world in the second quarter of the fifth century. It came to be called the Nestorian controversy, and how much of it was theological and how much political is still being debated, but it irreversibly split the church not only east and west but also north and south and cracked it into so many pieces that it was never the same again. Out of it came an ill-fitting name for the church in non-Roman Asia, "Nestorian."(Moffett pg 169)
He describes the geographic scope of this church, first of all, which extends from Syria up along the "Old Silk Road" through Edessa in what is now the town of Urfa, "a dusty town in eastern Turkey just north of the Syrian line," through Nisibis (one of the great "schools" of the early church), through names we know such as Mosul, Tekrit, Seleucia-Ctesiphon (just south of modern Baghdad), and easward through Persia, Afghanistan, and eastward to China.
What was striking for me was Moffett's description of "the Great Persecution," which didn't happen in the Roman empire at all, but rather, in the churches of Persia (which included modern Iraq), which began in around 339 and extended through to the year 400, in which "as many as 190,000 Persian christians died in the terror. It was worse than anything suffered in the West under Rome, yet the number of apostasies seemed to be fewer in Persia than in the West, which is a remarkable tribute to the steady courage of Asia's early Christians." (145)
Interestingly, this persecution was set off by Constantine's conversion to Christianity. "It was enough to make any Persian ruler conditioned by three hundred years of war with Rome suspecious of the emergence of a potential fifth column. Any lingering doubts must have been dispelled when about twenty years later Constantine began to gather his forces for war in the East... Faced with what seemed to be a double threat, a threat not only to national security but to the national religion as well, Persias priests and rulers cemented their alliance of state and religion in a series of periods of terror that have been called the most massiver persecution of Christians in history, "unequalled for its duration, its ferocity and the number of martyrs." (138).
It should be noted that this all occurred before the council of Ephesus, before the Schism. There is no way to say "these are not our people."
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Philip Jenkins, in his work "The Lost History of Christianity" (New York: HarperCollins, 2008) goes into some more detail about the scope of the church in this world before describing how it "dies".
To appreciate the scale of the Church of the East, we can look at a list of the church's metropolitans -- that is of those senior clergy who oversaw inferior hierarchies of bishops grouped in provinces. In England, to give a comparison, the medieval church had two metropolitans: respectively, at York and Canterbury. Timothy (a bishop of the eighth century) himself presided over nineteen metropolitans and eighty-five bishops. Though the exact locations of the metropolitan seats changed over time, map 1.1 on page 12 identifies some of the leading centers. Just in Timothy's lifetime, new metropolitan sees were created at Rai near Tehran, and in Syria, Terkestan, Armenia, and Dailumaye on the Caspian Sea.Maybe our "mental maps" omit this information because it is just simply too painful to recollect. "When Timothy died in 823, he had every reason to hope for his church's future" (19)
The presence of metropolitan seats in Turkestan and central Asia is amazing enough, but the list of bishoprics and lesser churches includes just as many shocks. Arabia had at least four sees, and Timothy created a new one in Yemen. And the church was growing in southern India, where believers claimed a direct inheritance from the missions of the apostle Thomas...
Timothy himself was committed to the church's further expansion, and he commissioned monks to carry the faith to the shores of the Caspian Sea, even into China. He reported the conversion of the Turkish great king, the khagan, who then ruled over much of central Asia. In a magnificent throwaway line, Timothy described, about 780, how "[i]n these days the Holy Spirit has anointed a metropolitan for the Turks, and we are preparing to consecrate another one for the Tibetans. Timothy was deeply conscious of the church's universality. When debating a technical liturgical question, he drew support from the practice of the wider churches of the sprawling Christian world he knew: the Persians and Assyrians don't do this, he argued, and nor do the churches of "the countries of the sunrise--that is to say, among the Indians, the Chinese, the Tibetans, the Turks." The church operated in multiple languages: in Syriac, Persian, Turkish, Soghdian, and Chinese, but not Latin, which scarcely mattered outside western Europe.
To put this geographical achievement in context, we might think of what was happening in contemporary Europe. Before Saint Benedict formed his first monsastery, before the probable date of the British king Arthur, Nestorian sees existed at Nisapur an Tus in Khurasan, in northeastern Persia, and at Rai. Before England had its first archbishop of Canterbury--possibly before Canturbury had a Christian church--the Nestorian church already had metropolitans at Merv and Herat, in the modern nations of (respectively) Turkmeistan and Afghanistan, and churches were operating Sri Lanka and Malabar. Before Good King Wenceslas ruled a Christian Bohemia, before Poland was Catholic, the Nestorian sees of Bukhara, Samarkand, and Patna all achieved metropolitan status. Our common mental maps of Christian history omit a thousand years of that story, and several million square miles of territory. (10-11)
But of course, the anger of the Muslims set off by the Crusades wreaked havoc among these churches. "Still, in 1050, [Asia Minor] had 373 bishoprics, and the inhabitants were virtually all Christian, overwhelmingly members of the Orthodox Church. Four hundred years later, that Christian proportion had fallen to 10 or 15 percent of the population, and we can find just three bishops. According to one estimate, the number of Asian Christians fell, between 1200 and 1500, from 21 million to 3.4 million. In the same years, the proportion of the world's Christians living in Africa and Asia combined fell from 34 percent to just 6 percent. Actually, the contraction outside Europe was probably more dramatic than even these figures suggest, but the basic point is accurate" (23-24).