Based on my knowledge of the Schism of 1054, that event precipitated the final separation between the Eastern Christian churches ( Michael Cerularius, the patriarch of Constantinople was the "leader" of this church) and the Western church (Pope Leo IX was the "leader" of this church). However before the Schism it sounded like they were already on bad terms with each other because they had different customs that the other church did not, customs that they did not agree with themselves.
Thanks to britannica for their extended knowledge on this matter and filling in the gaps the class left. I do not own the rights to the material, all credit goes to britannica.com.
