The Christian communities of South-West Asian countries were 'Eastern Churches' in relation to Europe since they were located to the east of Europe.

The Gospel was later taken to Rome, the capital of the Roman Empire and center of government where the emperor resided. When Emperor Constantine gave the Church freedom by the Edict of Milan in 313 after a long period of persecution, the Church gradually spread in the empire and moved further westwards. Rome became the center of the Church as well.

But in 330, Constantine moved the capital to Byzantium, rebuilt the city and called it Constantinople (Istanbul since 1930). The city lay on the eastern borders of Europe where Europe and Asia met. The Church grew in Constantinople and spread into the neighbouring countries of Eastern Europe. The presence of the emperor in Constantinople gave the city added prestige and political, social and cultural importance. Later the see of Constantinople became a patriarch as was the patriarchate of Rome, the former in Eastern Europe and the latter to the west of it. Thus arose a distinction, basically geographical, between the Eastern Church and the Western Church.

The distinction was heightened by cultural differences between the two. The Western Church adopted Latin as its liturgical language while in the Eastern Church it was Greek. Christian Rome was influenced by Latin literature and Roman culture and Constantinople by Greek literature and culture. Conflicts arose between the two Churches between Rome and Constantinople, which went on for several centuries, and finally in 1054 the break between them took place, the Greek Church calling itself 'Orthodox' while the Western Church continued to be called Catholic.

Other Churches, mainly in Eastern Europe and associated with Constantinople also broke away from Rome. The liturgy of the Greek rite had been inherited by them but adapted in Slavonic, Estonian, Arabic and other languages. Loosely linked to the patriarchate of Constantinople were several other autonomous Churches such as the Russian Orthodox Church.

The Orthodox Churches reject the jurisdiction of the Bishop of Rome, the Pope. The Catholic Church regards the Orthodox Churches as schismatic, that is they have the same doctrinal teachings as in the Catholic Church and valid sacraments but repudiate papal authority.

Eastern Churches that have returned to communion with the Catholic Church are called Eastern Catholic or uniate. Almost in every respect, apart from obedience to Rome, they resemble their Orthodox counterparts.

The Eastern Catholic or Uniate Churches have their own liturgical languages and rites, as, for instance, the Melchite (Greek Uniate), Maronite, Coptic, Chaldean, Armenian, Syrian and Malanakarese (Malabar) rites.

The Eastern Catholic Churches, which are called also as Oriental Churches, are governed by a special Curial department of the papacy, the Congregation for the Oriental Church, and have their own Code of Cannon Law. The Code for the Western or Latin Church makes it a point to say right at the beginning: "The canons of this Code concern only the Latin Church: (Can. 1)

Among the documents of Vatican II there is one specially for Eastern Churches: Decree on Eastern Catholic Churches. The following words of the decree are noteworthy: "History, tradition and numerous ecclesiastical institutions manifest luminously how much the universal Church is indebted to the Eastern Churches. This sacred synod, hence, not only honours this ecclesiastical and spiritual heritage with merited esteem and rightful praise, but also unhesitatingly looks upon it as the heritage of Christ's universal Church." (5)

Of the unity between the Churches, Eastern and Western, in the Catholic fold, the decree says: "Between these, there flourishes such an admirable brotherhood that this variety within the Church in no way harms her unity but rather manifests it.Individual Churches, whether of the East or of the West, although they differ somewhat among themselves in what are called rites (that is, in liturgy, ecclesiastical discipline, and spiritual heritage) are, nevertheless, equally entrusted to the pastoral guidance of the Roman Pontiff, the divinely appointed successor of St. Peter in supreme governance over the universal Church." (2,3).