This conflict was precipitated by the opposition of Roman Catholic Pope Nicholas I (r. 858-867) to the appointment by Byzantine Emperor Michael III of a lay scholar as Patriarch Photius I of Constantinople. The schism effectively ended in 867 with both the death of Pope Nicholas I and the first deposition of Photius. Nevertheless, it took two councils at Constantinople (869-870 and 879-880) to fully resolve the situation.
The controversy also involved Eastern and Western ecclesiastical jurisdictional rights in the Bulgarian church, as well as a doctrinal dispute over the Filioque (“and from the Son”) clause that had been added to the Nicene Creed by the Latin church, which was the theological breaking point in the eleventh century Great East-West Schism.
- ↑ "Union of Christendom". Catholic Encyclopedia. New York: Robert Appleton Company. 1913. http://en.wikisource.org/wiki/Catholic_Encyclopedia_(1913)/Union_of_Christendom.