Photian schism
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Photian schism is a term for the 9th-century-AD controversy between Eastern (Byzantine, later Orthodox) and Western (Latin, Roman Catholic) Christianity that was precipitated by the opposition of the Roman Pope John VII to the appointment by the Byzantine emperor Michael III of a lay scholar as Patriarch Photius I of Constantinople.
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 ultimate XIth century Great East-West Schism.