Within the Christian household, Orthodox also experienced serious divisions. The efforts to produce a unified Christianity beginning in the 4th Century CE did produce a remarkable amount of agreement among a very diverse Christian movement. However the heavy handed practices of the Byzantine Greek empire ultimately led to many of the non-Greek Christians splitting away from the Imperial Church. With the rise of Islam in the 7th Century CE, these non-Greek Christians hoped they could maintain their regional and ethnic differences under Islamic domination which also meant shaking off Greek Imperial Christianity. The formation of the “Oriental” Orthodox Churches such as the Coptic church, the Nestorian and Jacobite Orthodox churches can partly be explained by the intermixture of theology and ethnic political rivalries.
The biggest split in Christendom as far as Orthodoxy is concerned however occurred between the Greek Christians of the Eastern Roman Empire and the Latin Christians in Western Europe, which under the Greeks eventually was for all practical purposes beyond the control of the Empire. Latins and Greek maintained their unity in the face of monophysitism and Nestorianism. However, the linguistic, cultural and geographic separation of the Eastern and Western Christians led to an increasingly separated Catholic Christianity. The differences in custom and practice led to serious debates between Greek and Latin Christians. With the movement of the capital of the Roman Empire to Constantinople, the Greek Christians became increasingly less concerned about the problems of their Latin co-religionists. Eventually with four of the ancient patriarchates being Greek speaking, and only Rome being Latin speaking, and with the rise of Charlemagne (800 CE) and the development of Western Christian kings who challenged the sole claims to Christian imperialism of the Greeks, Rome turned to these new Kings for help in defending Western Christendom. With theological and liturgical differences, the support of Western Emperor claimants, Rome as the unrivaled patriarchate of the West claimed supremacy over the Greek bishops. This eventually led to further fights about theology and ecclesiology, and a permanent division in Christendom between the Greek East and Latin West. The Western Crusades of the 11-13th Centuries brought a Latin Christian army into military conflict with Greek civilians and the Byzantine army. Ultimately the sacking of Constantinople by the army of the 4th Crusade in 1204 was seen by most Greek Orthodox as the permanent divide between Greek and Latin Christians.
This conflict in Christendom now escalated to open warfare led Christians both East and West to see the others as enemy to their faith. This division in Christendom continued through the centuries and remained hostile and militaristic especially between the Russian Orthodox and Polish Catholics, and throughout the Balkans where Serbian Orthodox battled Croatian Catholics.
In the modern world, the Orthodox deprived of the defense of their kings and emperors have often felt neglected and abused by Christians of the West especially as they suffered under first Islamic rule and then later under atheistic communism.
Modern dialogue between Roman Catholic and Greek Orthodox Church leaders has led to a reduction of animosity, at least on paper, as the two sides agreed to withdraw mutual excommunications. But little has been accomplished, especially among the Orthodox in terms of church union because the Orthodox continue to suspect Roman Catholicism does not seek unity with the Orthodox but rather domination over the Orthodox.