The OEcumenical Councils 

As noted previously, the huge theological issues of the day were addressed by the emperors in Constantinople. These meetings were held exclusively in the eastern portions of the Empire.  It is incorrect to assert that the catholic, "Universal", Church first split in 1054 (The Great Schism). Below is a summary of each Ecumenical Council chronologically. Before we begin, a fact needs to be stated. heresies are never completely quashed. Of all the heresies ever practiced in the past, each sadly is being practiced somewhere in the world today. The Ecumenical Councils are: 

                                                                                                                        A) First Nicaea (325): 

The word "Uncreated" is critical to understanding what First Nicaea addressed. The priest Arius of Egypt began teaching that Christ's nature was not eternal, that He had been created. The bishops at First Nicaea said no, that Christ was not created, and He is Co-Eternal with God the Father and God the Spirit. The Council Fathers (the bishops in attendance) surely drew on Philippians, Chapter 2 and the Gospel of John, Chapter 1 to help their decision-making abilities.  A permanent method of calculating the dates of Easter/Pascha was also agreed upon. 

                                                                                                                   B)  The First Council of Constantinople (381)

This council was not elevated to an Ecumenical until centuries later, as there was no Roman presence. It was called to refine the orthodox statements some fifty years before.  Constantine's son was Arianian and for all practical purposes an Arian possessed the episcopal seat at Constantinople, so despite appearances of amplifying Nicaean Orthodoxy, Nicaean Orthodoxy was in scripto et in uso quite in danger. Roman legates should have been at the Council. Not only was the question of Arianism formally solidified (the Council Fathers could have chosen Arianism as the official dogma), but the Council's third cannon set the stage for seven centuries of disagreement:  it proclaimed that the See of Constantinople (founded by Andrew) is second only to the of Rome. Starting with Leo the Great, many Roman pontiffs took issue with such a closeness between the two See's.

                                                                                                                      C) The Council at Ephesus (431) 

This Council theoretically was to focus primary on the nature of Mary, but it was the first of several consecutive Councils where politics and semantics factored heavily into the votes; Cyril of Alexandria, the presider, was a long-term foe of the persons he was attempting to condemn., namely Diodorus of Tarsus, Theodore of Mopseustia, and Nestorius, (the leaders of the Antiochan School). These leaders were largely from lands East of the official boundaries of the Roman Empire. Saint Thomas the Apostle had brought Christianity to these lands; their liturgy was distinct, as was the language used in the Church of the East's liturgy. The Church of the East (the Assyrian Church) never used the word Christokos in their liturgy, as it was a Greek word. The Church of the East used and uses Aramaic in their public prayers (liturgy).  The specific language for Mary used in the liturgy of the Church of the East is "Mother of Christ our Lord and Savior" with the word for "Lord" being "MarYa":Lord God. Thus "Mother of Christ our Lord God and Savior" and for all intents and purposes the same as Theotokos "God-bearer" in Greek.