Eastern Catholics are the members of those churches in Eastern Europe and the Near East (and now in our own country) that are in full communion with the See of Rome and have the identical faith and morals possessed by Western Catholics of the Latin Rite.
They are the heirs of the partial unions with the Holy See made by Eastern Bishops from the 12th-16th centuries who sought to restore their ancient unity with the See of Peter. That unity, which existed before the separation of the churches of the West and East, had been disrupted by theological quarrels and by the medieval Crusades, especially the Latin occupation of Constantinople in 1204 A.D.
Eastern Catholics constitute many nationalities who by ancient tradition use rites, ceremonies, and languages in their church services that are quite different from those of their fellow Catholics of the Roman or Latin rite. In the words of a Catholic specialist on the Eastern churches, "one fundamental characteristic of Eastern Catholics is that their liturgical and canonical traditions are non-Latin". The East did not receive the Catholic Faith as daughter-churches of Rome, but directly from the Apostles via 4 great centers of Christian life within the Eastern part of the Roman Empire (Alexandria, Antioch, Jerusalem and Constantinople). Beyond the frontier of the Roman world were the national churches of Persia and Armenia where in the 5th century the Nestorian and Monophyite heresies unfortunately flourished, giving rise to churches calling themselves "Oriental Orthodox" and which would separate from the communion of the great Catholic Church. Nestorians who rejected the Council of Ephesus (431 A.D.) are still found in Syria, Iraq, and Turkestan. Monophysites who rejected the Council of Chalcedon (451 A.D.) are still found among the Egyptian Copts, Ethiopians, Syrians, and Armenians. Thus, interestingly, there are Eastern Christians who remain separated from both the Catholic Church and the Eastern Orthodox communion.
The Eastern Orthodox churches are a confederated grouping of some 16 or so independent ("autocephalous") national churches found largely in Eastern Europe, the Balkans, and the Near East, and immigrated into the nations of the West.
Possessing a valid hierarchy of bishops, priests, and deacons, with the monastic and ascetical life held in especial esteem, the Eastern Orthodox churches are the heirs of a lamentable separation from Rome which became hardened after the rejection of 2 great Reunion Councils (Lyons 1274 A.D. and Florence 1439 A.D.) which sought to heal the schism between Rome and Constantinople. The separation of these two great Sees represented a long process beginning with theological and liturgical quarrels in the 9th century, growing discord by 1054 A.D. marked by personal excommunications between Cardinal Humbert and the Patriarch Michael Cerularius, increased political and cultural and linguistic estrangement, and then actual ruptures in communion because of perceived dogmatic differences (especially over the Latin addition of "filoque" ["and the Son"] to the Creed). Finally, there occurred formal schism. Though the Eastern Orthodox lack adherence to the visible head of the Church Militant instituted by Christ for His One Church (the Bishop of Rome, the Successor of Peter), it is an immeasurable blessing that they retain almost all the faith, worship and spiritual practices which characterized the "undivided Church" of the 7 Ecumenical Councils.
Among the heads of these autocephalous Eastern Orthodox churches the "Ecumenical" Patriarch of Constantinople occupies a "primacy of honor" though this has been challenged for some time by the largest Eastern Orthodox church, the Russian Orthodox church under the Patriarch of Moscow. The other important patriarchs of the Eastern Orthodox bloc of churches are the patriarchs of such ancient sees of Alexandria, Antioch, and Jerusalem, followed in time by the later patriarchs of Rumania, Serbia, and Bulgaria, and the Catholicos-Patriarch of Georgia. The Church of Greece is headed by the Metropolitan Archbishop of Athens, and the smaller churches such as Cyprus, Finland, Albania, and Japan have each their own Archbishop. Some of the above churches have daughter-churches in the United States.
As we see, the Eastern Orthodox world is made up of 16 autocephalous or autonomous churches. Those of the Byzantine Greek tradition are Constantinople, Alexandria, Antioch, Jerusalem, Cyprus and Greece. In the Byzantine Slav tradition are found the churches of Russia, Poland, Finland, Czechoslovakia, Rumania, Bulgaria, Serbia, Albania, Georgia, and Estonia. The Byzantine Greek liturgy of St. John Chrysostom sung in different languages is practically universally celebrated among all these churches. This magnificent liturgy developed at Imperial Constantinople and enriched by the customs of Syrian Antioch and Palestinian Jerusalem was to spread throughout the Christian East, and into Slavonic lands, and is now found all over the world (being celebrated by both Eastern Catholics and the larger number Eastern Orthodox).
For centuries before the rupture of full communion between Rome and Constantinople occurring after 1204 A.D. (though there were parts of the East which remained in communion with the See of Peter, and there were even unionist patriarchs deploring the schism), the Bishops of the orthodox East and the orthodox West proclaimed a common Catholic faith safeguarded by the 7 Ecumenical Councils. When dogmatic disputes over the Procession of the Holy Spirit and the Latin use of unleavened bread in the Eucharist began to poison relations between the churches of Rome and Constantinople, and when the universal jurisdiction of the Pope as Peter's successor in the Primacy began to be questioned by medieval Byzantine theologians, one of the greatest tragedies in the history of Christianity was to occur - namely, the Byzantine Greek Schism from Catholic Unity.