Protestantism, Roman Catholicism, and Eastern Orthodoxy all fall under the secular umbrella of Christianity. While it is true that there may be SOME similar theological doctrines, the development and practices are vastly different. For a great study on the history of the reformation and how the Protestants split from Roman Catholicism watch the 14-part series “Protestant Reformation” by Dr. Andy Woods at the link below.
The Greek [Eastern] and Roman [Western] churches were never geographically unified under one government and from the very beginning differed considerably in terms of nationality, language and various ceremonies. The council at Nicea in 787 is regarded by many Orthodox as the last truly ecumenical council between East and West. During the period from the 9th to the 11th centuries the estrangement between the churches grew. Many factors have been suggested to account for this estrangement. Culturally, the differences in language and practice of the liturgy have been postulated. Politically, the alliances of the Byzantine (Eastern) empire with the patriarch of Constantinople and the new German empire (West) with the bishop of Rome appear to have also contributed to the isolation of the churches. Ecclesiastically, the issues of the primacy of the Roman See and distinctives concerning Eastern liturgy and priesthood only further complicated the already tenuous relationship.
The seventh ecumenical council at Nicea provided the climax of the iconoclastic controversy. Eastern emperors set themselves against the practice of veneration of idols… Difficulties in communication ensued between East and West. Neither patriarch nor pope spoke the other’s language. The matter was further complicated by efforts on the part of both East and West to reach the Slavs. Moravia and Bulgaria became a bone of contention in these efforts. King Boris of Bulgaria first accepted the dominion of Byzantium, then turned to Rome to see if he could receive more favorable terms. When Nicholas I sent bishop Formosus of Porto to reorganize the new Bulgarian church, the Byzantian church protested the doctrinal emphases of the West (specifically that the filioque clause was added to the Nicene Creed) and diplomacy between the churches was strained even further.
John A. Jelinek (1990). Michigan Theological Journal, 1(1), 69–77.
In the time which follows the period of the great councils it will be convenient to consider the East separately from the West. Such a division is not a matter simply of order and system. For the characteristics of Eastern minds and of Eastern theology differ widely from those of the West. In the East till the ninth century there is more tendency to speculation, more power of theological instinct, more capacity for realizing abstract truth. In the West there is a love of the concrete and the practically useful and efficient, a desire to make sharp distinctions and press alternatives, a fuller regard for considerations of common sense. And the controlling powers are different in these different part of the Church. In the East the authority of the Church as a whole, expressing its voice by means of conciliar decisions which the Christian community accepts and ratifies, continues to be a dominant force. In the West the government of the Church passes more and more into the hands of the Popes, though councils and the collective acceptance of doctrine continue to exist. In the East the power of the State over the Church reaches a degree which the position of the Papacy prevents in the West. In the East from the ninth century conservatism is stronger; and enterprise is greater in the West. Marked differences of character and general history, of which these are representative, necessarily affect the maintenance and development of particular doctrines, and among them of the Eucharist. And from at any rate the eighth century onwards the special form taken by the veneration of images in the East has had an important bearing on some matters connected with Eucharistic doctrine.
Stone, D. (1909). A history of the doctrine of the holy eucharist (p. 133). London: Longmans, Green, and Co.
In 1054 Pope Leo IX sent Cardinal Humbert of Silva Candida with a delegation to the Patriarch of Constantinople (then Michael Cerularius) to discuss problems between Rome and Constantinople. Cerularius rejected the delegation, the papal claims, and the filioque clause. The Western legates responded by declaring that Constantinople had altered the Nicene Creed. Mutual excommunications followed these accusations. Cardinal Humbert posted a bull of excommunication against Cerularius on the altar of the Hagia Sophia at the time of the Divine Liturgy, July 16, 1054. Cerularius retaliated by summoning the permanent synod which anathematized the authors of the bull and the document itself.
It is evident that the nearly simultaneous anathemas were not the final cause of the schism, though some might argue that they provided the formal cause. [The Eastern and Western church was formally split]
As the Muslim Turks advanced on the Byzantine Empire in the Middle Ages, the Eastern churches looked to the West for help. The relief came in a surprising manner when an army of crusading knights [under the banner of Rome] sacked Constantinople in 1204. The Eastern Patriarch was forced to retreat to Nicea until the eventual recapture of the City. The embitterment resulting from this hostile act undermined the attempts of the West to establish renewed relations.
John A. Jelinek (1990). Michigan Theological Journal, 1(1), 69–77.
On May 29, 1453 the Ottoman Sultan Mehmed conquered Constantinople. Thousands of Christians were murdered and raped, as ancient churches of the city were plundered, their altars were stripped. The capitol of the Eastern Church, the Hagia Sophia, was turned into a mosque. Roman Catholic Pope Nicholas V, who reigned from 1447 to 1455, was unable to muster any support for Emperor Constantine XI Palaiologos.
Christianity is a complex faith, and its consequences differ in differing contexts. What I have said may well apply to the medieval West, where in fact technology made spectacular advances. But the Greek East, a highly civilized realm of equal Christian devotion, seems to have produced no marked technological innovation after the late seventh century, when Greek fire was invented. The key to the contrast may perhaps be found in a difference in the tonality of piety and thought which students of comparative theology find between the Greek and the Latin Churches. The Greeks believed that sin was intellectual blindness, and that salvation was found in illumination, orthodoxy—that is, clear thinking. The Latins, on the other hand, felt that sin was moral evil, and that salvation was to be found in right conduct. Eastern theology has been intellectualist. Western theology has been voluntarist. The Greek saint contemplates; the Western saint acts. The implications of Christianity for the conquest of nature would emerge more easily in the Western atmosphere.
Schaeffer, F. A. (1982). The complete works of Francis A. Schaeffer: a Christian worldview (Vol. 5, p. 65). Westchester, IL: Crossway Books.
“Coptic” means “Egyptian,” and Christians living in Egypt identify themselves as Coptic Christians. As a denomination they originated in the city of Alexandria, one of the most faithful, respected, and fruitful cities during the Apostolic Period. Proudly, the Coptic Christians acknowledge and herald John Mark, (author of the Gospel of Mark), as their founder and first bishop sometime between A.D. 42 - A.D. 62. The Coptic Church was actually involved in the very first major split in the Church, well before there was such a thing as "Roman" Catholicism, and it was also well before the East/West split.
Prior to the “Great” East/West Schism of A.D. 1054, the Coptics were separated from the rest by the Council of Chalcedon in A.D. 451. The council met to discuss the Incarnation of Christ and declared that Christ was "one hypostasis in two natures" (i.e., one person who shares two distinct natures). This became standard orthodoxy for Eastern Orthodox, Roman Catholic, and Protestant churches from then on. The Coptic understanding is that Christ is one nature from two natures: "the Logos Incarnate." In this understanding, Christ is from, not in, two natures: full humanity and full divinity. Some in the Coptic Orthodox Church believe that their position was misunderstood at the Council of Chalcedon and take great pains to ensure that they are not seen as Monophysitic (denying the two natures of Christ), but rather "Miaphysitic" (believing in one composite/conjoined nature from two). Some believe that perhaps the council understood the church correctly, but wanted to exile the church for its refusal to take part in politics or due to the rivalry between the bishops of Alexandria and Rome. To this day, 95 percent of Christians in Alexandria are members of the Coptic Orthodox Church.