The greatest military challenge to the Eastern empire was the rise of Islam. When Mohammed died in 632, his followers carried their faith with the sword into the Persian and Byzantine empires. Major centers were lost to the Muslim hordes: Damascus fell in 635, Jerusalem in 638, Caesarea in 640, and Alexandria in 641. As the Muslims swept across North Africa and into Spain, they were finally stopped by Charles Martel and the Franks in 732, but in the Eastern empire they continued on up into the Balkans. As time went by, this caused more and more isolation of the East from the West.
“When the Goths swept down upon Rome, that city turned for help - not to Constantinople, but to the Franks; in gratitude for his aid the pope crowned Charles the Great - Charlemagne - emperor on Christmas Day in 800, and the Roman Church became coterminous with the Holy Roman Empire.” (Frank S. Mead, Handbook of Denominations, p. 183). Due to the leadership of the Roman Bishop holding the western empire together, the Roman bishop was able to provide the spiritual leadership for all those under the new government of Charlemagne. This met with resistance and resentment in the East.
According to Reardon, “The causes of the break between Eastern and Western Christianity were complex, but the chief one was probably the Roman Papacy. The political disintegration resulting from the barbarian invasions solicited a strong, highly centralized form of oversight in the Western Church, and Rome was the only one of the original patriarchs found west of the Adriatic Sea. As more and more problems in the West were referred to the Roman Papacy for adjudication, Rome’s recognized authority grew. This authority was considerably aided by certain forged documents, one of which purported that Constantine had given the government of central Italy into the hands of the Roman Pope. In the East, meanwhile, marked by greater political unity and stability, the Church felt no need for such centralized oversight.” The History of Orthodox Christianity, p. 20)
The Roman Pope and the patriarch of Constantinople continued in conflict over various matters. “In 857 Ignatius, in Constantinople, refused to administer the sacrament to Caesar Bardas on the ground that he was immoral. Tried and imprisoned by the emperor, Ignatius was succeeded by Photius…” (Mead, p.183). Pope John VII opposed the appointment of Photius, who in his turn refused to accept the supremacy of the pope in the Eastern Church. When the Latin delegation at his council of his consecration pressured Photius to accept the filioque to get their support, he refused that also. More controversy developed over ecclesiastical jurisdictional rights in the Bulgarian church.
In the tenth century Vladimir, grand prince of Kiev and of all Russia converted to Christianity. His envoys to Constantinople were captivated by the Church of Holy Wisdom and the liturgy.
In 1054 what is known as the “Great Schism” took place between Rome and Constantinople when the pope excommunicated the Eastern Patriarch and was in turn excommunicated himself by the Patriarch. The primary doctrinal issues were the filioque clause and the authority of the pope. Other issues included the dates for Easter, priestly celibacy, disagreements over different Lenten practices, and the type of bread to use for the Eucharist.
Further separation was caused by the sacking of Constantinople by the Fourth Crusade in 1204, including the sacking of the Church of Holy Wisdom. “The Crusades, which had been called to fight against the Moslem invaders, also turned the sword against the Orthodox Christians in the East.” (Reardon, p.21) The Orthodox Church was suppressed in its own capital for the next 50 years.
“As Moslem forces began to take the territory all around Constantinople, Byzantine emperors pleaded for military help from fellow Christians in the West. In response to these pleas, Rome summoned a synod of reunion at the city of Florence in 1439. Eastern Orthodoxy’s small delegation, including the Emperor, the Patriarch of Constantinople and a few bishops, capitulated to Rome’s insistence on the filioque and the supremacy of the Roman Pope over all of the Church. This “Union of Florence” was immediately and universally rejected in the East, nor did it bring very many Christians from the West to fight for the survival of Byzantium.” (Reardon, p.21)
In 1453 Constantinople finally fell to the Ottoman Turk Muslims, and the Byzantine empire ceased to exist. “After eleven centuries, the original Christian empire was at an end, and the Christians became a minority in a community run by Muslims. Without an emperor as their head, they looked to the patriarch for political guidance. Muslims tended to follow the Christian lead and consider him the spokesman for the Christian community.” (Shelly, p.150)
After the fall of Constantinople, leadership of the Eastern church flourished in Russia. “Over the years Russia made the aesthetic glories of Orthodox Christianity her own. Gradually Moscow came to see herself as the leader of the Orthodox world. A theory developed that there had been one Rome, in Italy, that had fallen to the barbarians and to the Roman Catholic heresy. There had been a second Rome: Constantinople. And when that fell to the Turks, there was a third Rome: Moscow. The emperor took his title from the first Rome - Tzar is the same word as Caesar — just as he had taken his religion from the second.” (Shelly, p.151)
Both the Roman Catholic and Eastern Orthodox Churches consider themselves to be the one true Christian church, both claiming direct apostolic succession, to the earliest church established by Paul. Unlike Roman Catholicism, Eastern Orthodoxy “is composed of several self-governing ecclesial bodies, each geographically and nationally distinct but theologically unified. Each self-governing (or autocephalous) body, often but not always encompassing a nation, is shepherded by a synod of bishops whose duty, among other things, is to preserve and teach the Apostolic and patristic traditions and related church practices.” (Wikipedia, Orthodox Church). “It is not a monarchy with one all-powerful ruler at the top, but ‘an oligarchy of patriarchs,’ based on the body of bishops and responsible to local or general (ecumenical) church councils. No one patriarch is responsible to any other patriarch; yet all are within the jurisdiction of an ecumenical council of all the churches in communion with the patriarch of Constantinople, who holds the title Ecumenical Patriarch.” (Handbook of Denominations, p.183).
To better understand the nature of Eastern Orthodoxy compared to Roman Catholicism in the way they operate as organizations, Reardon gives a good explanation:
“A single illustration may serve the purpose. When monks from Rome established their mission in England, centered at Canterbury, near the end of the sixth century, they continued to remain under the immediate jurisdiction of the Roman Pope and their language in worship continued to be Latin. The same pattern attended the missionary work in Gaul, Germany, Scandinavia and elsewhere in the West. Latin was the language of worship in all these churches (until Vatican II in the early 1960’s), and Rome endeavored with varying success to gain and retain appointment of local bishops. By and large the latter is still the case today.
“Such centralization and uniformity did not characterize the historical development of Eastern Orthodoxy, as we may see in the matter of language. Notwithstanding the dominance of the Greek tongue throughout the Byzantine Empire, there had always been Eastern Christians who worshiped in Syrian, Ethiopian, Coptic and eventually Arabic; so as Orthodox missionaries moved northward it was understood from the beginning that the native tongues of the new regions would be the languages used for worship and life of the new congregations. In fact, since these native languages had never previously been written down, the missionaries themselves were obliged to elaborate a new alphabet for them and commenced their literature from scratch. One should keep in mind that between the Slavic mission of 863 and the Alaskan mission of 1793 the Orthodox Church put the Gospel into nearly 3 dozen languages that had never been written down before.” (The History of Orthodox Christianity, pp. 23-24)
This idea of keeping the individual cultures where the Gospel was preached by Eastern Orthodoxy leads to branches known as “Russian Orthodox,” “Greek Orthodox,” etc (although often the whole denomination is called “Greek Orthodox“). There have even been schisms over the centuries based on some doctrinal issues so that there are also sects called Oriental Orthodox (Coptic and Syrian Orthodox, e.g.)
I hope this short history lesson demonstrates that Rome became the leading church not because of any foundation of Christ, but a foundation in the Roman Empire’s political system. The Eastern Orthodox Church received its headship in the very same way. Neither are the successor to the New Testament Church.