What is the “Great Schism” of 1054 mainly about?

The story behind the answer

In 1054, mutual excommunications between Cardinal Humbert (for the pope) and Patriarch Michael Cerularius (for Constantinople) formalized a long‑simmering rift between the Latin West and the Greek East. Core tensions included papal supremacy versus a conciliar model of leadership, the Western addition of the Filioque to the Nicene Creed, and divergent liturgical practices (like unleavened vs. leavened bread). Political rivalries between Rome and Constantinople compounded the theological disputes.

This was not about Protestant reformers—that upheaval came in the 1500s. The divide deepened after the Fourth Crusade’s sack of Constantinople in 1204, leaving lasting mistrust. Though the mutual excommunications were lifted in 1965 by Pope Paul VI and Patriarch Athenagoras I, the two traditions remain separate churches that share ancient roots but differ in governance and certain doctrines.