Cathedral and Church History

The Church did not "split" into Catholic and Orthodox, the Eastern Churches definitely split in the 11th century from the Church, and are now referred to as the "Orthodox". Since that time, all most all of them have split again, with part of each returning to the Catholic Church from which they split. There can be only one Church as it is the Mystical Body of Christ and His Bride, and He is neither Schizophrenic nor a bigamist.

When the Eastern Churches left the authority of Rome it was referred to as the Eastern Schism. "The Great Schism" happened centuries later when the pope moved to Avignon. THAT is what the Church refers to as the Great Schism.

from A Catholic Dictionary, edited by Donald Attwater, Second edition, revised 1957

The Great Schism, otherwise know as the Schism of the West was not strictly a schism at all but a conflict between the two parties within the Church each claiming to support the true pope. Three months after the election of Urban VI, in 1378, the fifteen electing cardinals declared that they had appointed him only as a temporary vicar and that in any case the election was invalid as made under fear of violence from the Roman mob. Urban retorted by naming twenty-eight new cardinals, and the others at once proceeded to elect Cardinal Robert of Geneva as Pope Clement VII, who went to reside at Avignon. The quarrel was in its origin not a theological or religious one, but was caused by the ambition and jealousy of French influence, which was supported to some extent for political reasons by Spain, Naples, Provence, and Scotland; England, Germany, Scandinavia, Wales, Ireland, Portugal, Flanders and Hungary stood by what they believe to be the true pope at Rome. The Church was torn from top to bottom by the schism, both sides in good faith (it was impossible to know to whom allegiance was due), which lasted with its two lines of popes (and at one time three) till the election of Martin V in 1417. It is now regarded as practically certain that the Urbanist popes were the true ones and their names are included in semi-official lists; moreover, the ordinal numbers of the Clementine claimants (who, however, are not called anti-popes,) were adopted by subsequent popes of the same name.

The Schism of the East the estrangement and severance from the Holy See of what is now called the Orthodox Eastern Church was a gradual process extending over centuries. After a number of minor schisms the first serious, though short, break was that of Photius; from then on tension between East and West increased, and the schism of Cerularius occurred in 1054. From then on the breach gradually widened and has been definitive since 1472. There was a formal union from the 2nd Council of Lyons in 1274 until 1282, and a more promising one after the Council of Florence from 1439 to 1472. After the capture of Constantinople it was in the Turkish interest to reopen and widen the breach with the powerful Roman church; the patriarchates of Alexandria, Antioch, and Jerusalem were dragged into this policy, Russia and the Slav churches stood out the longest of any: none of these churches, except Constantinople itself in 1472, formally and definitely broke away from the unity of the Church. But in the course of centuries the schism has set and crystallized into a definite separation from the Holy See of many million people with a true priesthood and valid sacraments. The origins, causes and development of the schism are matters of much complication, still not fully unraveled.

from Modern Catholic Dictionary by John A. Hardon, S.J. Doubleday & Co., Inc. Garden City, NY 1980

Separation of the Christian Churches of the East from unity with Rome. The schism was centuries in the making and finally became fixed in 1054, when the Patriarch of Constantinople, Michael Cerularisu (died 1059), was excommunicated by the papal legates for opposing the use of leavened bread by the Latin Church and removing the Pope’s name from the diptychs or list of persons to be prayed for in the Eucharistic liturgy. A temporary reunion with Rome was effected by the Second Council of Lyons (1274) and the Council of Florence (1439) but never stabilized.