It's no secret that Catholics and Orthodox Christians belong to the same religion - Christianity. But when, and most importantly, why did Christianity split into these two main streams? It turns out that, as always, human vices are to blame, in this case the heads of the church, the Pope and the Patriarch of Constantinople, could not determine which of them is more important, and who should obey whom.
In 395, the division of the Roman Empire into Eastern and Western took place, and if the Eastern for several centuries was a single state, then the Western soon disintegrated and became the unification of various Germanic principalities. The division of the empire also affected the situation in the Christian church. Gradually, the differences between the churches in the east and the west multiplied, and over time, relations began to heat up.
In 1054, Pope Leo IX sent legates to Constantinople, led by Cardinal Humbert, to resolve the conflict, which began with the closure of the Latin churches in Constantinople in 1053 by order of Patriarch Michael Kerularius, under which his sacellary Constantine threw out of the tabernacles the Holy Gifts prepared by the western custom of unleavened bread, and trampled them underfoot. However, it was not possible to find a way to reconciliation, and on July 16, 1054, in the Cathedral of Hagia Sophia, the papal legates announced the deposition of Cerularius and his excommunication from the Church. In response, on July 20, the patriarch anathematized the legates. That is, the heads of the church took and excommunicated each other from it. From that moment on, the united church ceased to exist, and the future Catholic and Orthodox churches cursed by each other severed relations for more than 900 years.
And only in 1964, in Jerusalem, a meeting was held between the Ecumenical Patriarch Athenagoras, Primate of the Orthodox Church of Constantinople, and Pope Paul VI, as a result of which in December 1965 mutual anathemas were lifted and a Joint Declaration was signed. However, the “gesture of justice and mutual forgiveness” (Joint Declaration, 5) had no practical or canonical meaning.
From a Catholic point of view, the anathemas of the I Vatican Council against all who deny the doctrine of the primacy of the Pope and the infallibility of his judgments on matters of faith and morality pronounced ex cathedra (that is, when the Pope acts as the “earthly head and instructor of all Christians "), as well as a number of other dogmatic regulations.
The term "Orthodoxy" or, what is the same, "orthodoxy" existed long before the division of the churches: Clement of Alexandria in the II century meant to them the true faith and like-mindedness of the whole church as opposed to dissent. The name "Orthodox" was consolidated behind the Eastern Church after the church schism in 1054, when the Western Church appropriated the name "Catholic", that is, "Universal".
This term (Catholicism) was used in ancient creeds as the name of the entire Christian church. Ignatius of Antioch was the first to call the church "catholic". After the division of the churches in 1054, both of them retained the name "catholic" in their self-names. In the course of historical development, the word "Catholic" began to refer only to the Roman Church. As a Catholic ("universal"), it opposed itself in the Middle Ages to the Eastern Greek Church, and after the Reformation - to the Protestant churches. However, almost all trends in Christianity have pretended and continue to pretend to be "catholic".