What (Who) are the Eastern Catholic Churches?
As early as the beginning of the 2nd century A.D. the famous Syrian bishop, Ignatius of Antioch, called the Christian Church “Catholic,” meaning, “Universal.” This was because (as the Greek root of that word implies) Christians were in unity all over the then known world. This unity lasted until the heresies of the 4th and 5th centuries began ripping apart the fabric of the Church.
During her early missionary expansion around the Mediterranean and into Persia and even into China and India, the Church adapted to the languages, customs, thought patterns and spiritualities of the areas in which she took root. Thus, while the early Catholic Churches agreed on the set of beliefs stated in the Creeds and celebrated in her diverse liturgies, these Churches appeared different in their outward expressions. Christians in Antioch celebrated the faith differently from those in Rome, and these in turn differed from Christians in Alexandria and the Kerala Coast of India and other places. Yet all were Churches of the Universal Catholic Church, a “Communion” of Churches. By Communion is meant here the bonds of faith and Christian love and mutual respect.
The 5th century was not the only time that Christians separated from mutual communion. The 11th century saw the “last straw” in a separation between Latin West and Greek-Byzantine East. This estrangement preceded the watershed date of 1054 A.D., and its final effect took place well afterwards in the destruction of Constantinople, home of the Byzantine Church. “Orthodox” became a formal name of the majority of Eastern Christians.
Between the Syrian, Egyptian, Persian, Armenian and Indian Churches that separated in the 5th century and the Byzantines in the 11th, the Second Millennium was a time when the majority of the East was estranged from Rome.
The only exceptions are the Maronite Catholics of the Middle East and the Italo-Albanian Greek-Byzantine Catholics of southern Italy. Both Churches claim never to have broken their communion with the See of Rome.
Beginning in the 16th century and even into the 20th, and for various reasons, groups of these separated Christians decided to re-establish communion with Rome. They were certainly not the majority within their individual Churches, but they were significant. These are what are today known as the Eastern Catholic Churches. Thus, all but the Maronites and the Italo-Albanians have Orthodox counterpart Churches.
(See Chapter 7 of CYT, especially the diagrams on pp. 90 & 98.)
I do have one comment: you write
The current Latin Church has deviated from the faith held by all Christianityh (regardless of rites of worship), as defined by the Seven Ecumenical Councils. If Maronite Catholics claim unbroken communion with Rome, I understand that to mean that the Maronites left the Communion of the other four Patriarchs and went with the Patriarch of Rome into schism.
The question is what makes you different from the Maronite Orthodox Church? Theology? Do you profess Filioque, accept Immaculate Conception and papal infallibility, or only some and not all?
Orthodox Churches all share the same theology to which, at one time, your church and Old Rome used to subscribe.