When Constantine the Great established a new capital on the European side of present-day Turkey in 325 c.e., it began a paradigm shift for citizens of the empire: The Roman Empire was no longer centered in Italy but in Constantinople.
This realization began to dawn upon the Christians who were increasingly running the empire. Thus began a sense of the Greek Church, for Constantinople spoke Greek and reflected a different approach to running the empire than the Latin and imperial administration of Rome.
Nonetheless, it is better to locate the East-West split in Christianity in the latter half of the first millennium c.e. than the first half. The early church was primarily unaware of regionalization for the first five centuries.
In fact, the Council of Chalcedon (451) organized the hundreds of bishoprics of the empire not by a Greek Church v. a Latin Church but simply by its recognition of historical prestige and dependency. There were five spheres of inﬂ uence among early Christians and so five patriarchates: Rome, Constantinople, Alexandria, Antioch, and Jerusalem—and precisely in this order were they prioritized.
Rome was always given pride of place among them, perhaps because it was the destination for Paul, the city of martyrdom for Peter, and the home of the caesars. Ironically enough, it was the church of Rome that always provided a defense of the "orthodox" position for Christians of the East in the early centuries of the faith.
There were always disputes among the bishops, but in the first half of the millennium Latin-speaking Rome and Greek-speaking Constantinople were not the disputants.
The patriarch of Rome, called the pope because of his "papa" stature, had jurisdiction not only over the Latin-speaking Western Roman Empire but over parts of the Greek-speaking East, even over Greece itself. The Eastern Roman Empire had a collage of languages among its Christian citizens, including Coptic in Alexandria and Syriac in Antioch and Jerusalem.
The emperors tried to impose unity among them all, but the Oriental Orthodox Churches of the Middle East were considered inferior partners in the empire. This second-rate status eventually influenced them to form their own churches.
By the time of Justinian I, the word orthodox was used to describe correct (orthos) belief (doxos) in official church teaching on the doctrines of the Trinitarian nature of God and the divine nature of Jesus (Christ) of Nazareth in the face of heretical positions.
It was not used to differentiate the Greek (Orthodox) Church from the Latin (Catholic) Church. This nuance of the Greek Church arose around the eighth or ninth century. An early challenge to unity between Rome and Constantinople occurred when John the Faster proclaimed himself as the "ecumenical patriarch" of Constantinople (582–595). This title may have been a challenge to the pope’s authority.
More significant for the prestige of both patriarchates were external factors like the Muslim invasions of Byzantine lands in the 600s c.e., and the consolidation of the Frankish tribes as the Holy Roman Empire (or Empire of the West) under Charlemagne.
The Greek Church always gave a special role to the emperor to mediate disputes and to summon councils for the sake of unity, an idea that modern historians call Caesaropapacy. The Latin Church, on the other hand, allowed its patriarch the pope to be more independent from secular authorities and to resolve disputes by himself.
Other small and divergent practices were goads in the process: Greeks allowed married men to become priests; the Latins increasingly sought celibates as priests; Greeks took communion with leavened bread, the Latins with unleavened bread; Greeks celebrated the same religious feasts as the Latins, but according to a different calendar. Oftentimes the two churches worked out agreements of toleration for their differences, but two issues hastened the day of divorce.
First, the Byzantine emperor Leo banned the use of certain religious images, a policy called iconoclasm. While large numbers of Greek Church members opposed this decree, the pope summarily rejected it and was punished with the forfeiture of his lands in the Greek-speaking world to the ecumenical patriarch of Constantinople. Even when the Greek Church resoundingly repudiated iconoclasm in the Second Council of Nicaea (787 c.e.), the pope did not receive his lands back.
Second, the resolution of the iconoclastic controversy so invigorated the Greek Church that it began to expand its presence in the Slavic world. It sent out the great missionaries Cyril of Alexandria and Methodius to spread the faith in Bulgaria and Moravia.
They greatly innovated religious customs of the church so that the Slavs could more easily accept Christianity. For example, they allowed the use of native languages in their religious services and writings instead of requiring traditional Greek, and they even concocted an alphabet that served this end.
The pope refused to recognize the jurisdiction of the ecumenical patriarch over these new mission fields. A compromise was worked out, but significant damage was done to the relationship between the two leaders.
With the tension already present for two centuries, it did not take much to cause the two churches to divide in an official and structural way in 1054. The issue in fact was quite minor: the use of unleavened bread in the Eucharist by the Catholics mentioned above, tolerated for centuries, now was exacerbated into a gaping chasm. The patriarch and the pope mutually excommunicated each other.
When Constantinople acted, its dependent mission lands sided with her; thus, the West found itself cut off from the Bulgarian, Serbian, and Russian churches, along with "Orthodox" Christians from Egypt and Syria. Now the Greek Church really became a separate institution, the Orthodox Church.
At first, most in the East and the West thought that the split would be temporary, just like other quarrels in the previous 300 years. The irreparability of the rupture, however, became apparent when crusaders invaded and sacked Constantinople in 1204 (called "the Rape of Constantinople").
The invaders stole cultural treasures, replaced Orthodox with Catholic bishops, and elevated a Latin bishop as the patriarch of Constantinople. Only Serbia and Bulgaria recognized this change in hierarchy, while the rest of the Orthodox world submitted to the Greek ecumenical patriarch in exile.
The bad blood spoiled any hope for reconciliation, though later efforts at the Council of Lyon (1274) and Council of Florence (1438–45) were made. As the Greek civilization weakened before the Muslim invaders, Orthodox and Catholic overtures were made to soften the mutual excommunications.
But always the rank-and-file members objected and agreements collapsed. The prevailing bitterness was so poisonous that the Orthodox members preferred to live under the Muslims than submit to the Catholics.
Under the Ottoman Muslims the sultan imposed the ecumenical patriarch as the spokesperson for all the Orthodox Christians in their empire. Through the compartmentalization of the Christians, the Ottomans could keep control of the church and enforce their bureaucratic standards. The Greek Church was too independent to embrace such uniformity.
As nationalism took hold in the Balkans and elsewhere, self-governing national Orthodox churches spun off, until finally the Ottomans were themselves expelled in the 20th century and the resentments of national Orthodox churches toward Constantinople were exposed.
Prophetic leadership for the Greek Church tended to come from its monastic base, especially from Mt. Athos. Top-down leadership rarely worked for the ecumenical patriarch in the same way as it did for the pope.
Central directives were issued primarily through synods and councils. The monks brought a form of mysticism into the Greek Church that pervaded many of its devotions, theologies, and art forms.
Monasteries had few institutionalized controls but functioned under spiritual masters known as abbots. In contrast, the Latin Church was influenced by the intellectual development of western Europe.
It had to give logical explanations and rational tests for many of its doctrines, and monasteries were not given the central role in the spiritual guidance of the church. Neither pope nor bishop nor monastery was spared the pastoral reforms that wrenched the whole Latin Church in later centuries.