Why did the church split in 1066?

Answer 1

Because of corrupt practices and false teaching in the Roman Catholic Church.

The protests against the corruption began in earnest when Martin Luther nailed his 95 Theses on to the door of the Castle Church of Wittenberg, according to university custom. Luther was excommunicated from the Roman Catholic Church.

After this first stage of the Reformation, following the excommunication of Luther and condemnation of the Reformation by the Pope, the work and writings of John Calvin were influential in establishing a loose consensus among various groups in Switzerland, Scotland, Hungary, Germany and elsewhere.

Answer 2

Catholic AnswerThe Schism of the East, often confusingly called the Great Schism (the Great Schism in the Catholic Church was the Western Schism, not the Eastern Schism) was primarily caused by historical and national interests. The Eastern Churches had been flirting with various heresies from about the fourth century onward. Vladimir Soloviev covers this rather well, in a short work entitled The Russian Church and the Papacy, (see link below). Vladimir Soloviev was one of the premier theologians from the 19th century, an intellect to rival the great St. Thomas Aquinas. He breaks down all the various heresies over the centuries, and concludes:

This was no matter of a dispute in theology or a rivalry between prelates. It was simply the refusal of the old empire of Constantinople to give place to the new Western power born of the close alliance of the papacy with the Frankish kingdom; everything else was secondary or by way of excuse. This view is confirmed when one recognizes that after Photius' death the schism did not take effect for a century and a half--exactly the period when Western Christendom, newly organized, seemed on the verge of collapse, when the papacy was subservient to a degenerate oligarchy and had lost is moral and religious prestige, and when the Carolingian dynasty was consumed with internal strife. But no sooner was the imperial power restored under the energetic government of the German kings, no sooner was the See of Peter again occupied by men of apostolic character, than the anti-Catholic movement of Constantinople broke forth with violence and the schism was consummated. 　

Historians usually record unleavened bread vs leavened, the filioque clause, etc. as the reasons for the schism, but Soloviev effectively demolished this argument.

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

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.