The Great Schism between East and West
The mutual excommunications of 1054, conventionally dated as the breach between East and West.
Medieval
c. 750 – 1100East and West divided in the Great Schism. Among the disputes was the Filioque — the Western addition of the words "and the Son" to the Nicene Creed's clause on the procession of the Holy Spirit, which the Eastern churches had not received and did not accept.
East and West divided in the Great Schism. Among the deepest causes was the claim of the bishop of Rome to a universal primacy of jurisdiction over the whole Church, which the Eastern churches honoured as a primacy of honour but did not accept as a supremacy.
The in-app commentary runs from the Fathers to the early-modern record, then stops — that's where the public-domain sources end, not where the reading does. For the modern reading, follow the sources directly.