What did the pope in Rome and the patriarch in Constantinople do to cause a long lasting schism in Christianity?

Answer 1

Catholic Answer

This was a long and terrible problem that became more and more complicated over time, the roots of it extending back to when the Emperor Constantine moved his capital from Rome to Constantinople, while the Holy Father remained in Rome.

There was no one thing that you can put your finger on, even though many try - for instance the use of leavened or unleavened bread, but this has never really been an issue, and both are approved of in the Western Church.

The underlying problem is that most of the Churches in the east came under government control to one extent or another and became really national "churches" with their bishops owing allegiance to their ruler rather than the Holy Father. This circumstance has continued, and worsened to this day. When things finally reached a head in the 11th century, they both excommunicated each other. This has been lifted several times, but reunion is still elusive.

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.

Answer 2

They excommunicated each other.