Divisions within religious traditions are usually described in doctrinal terms afterwards. The proximate causes more often concern authority, practice and the circumstances in which a decision was taken.
Authority questions do the dividing
Disputes that split communities tend to concern who may decide: which office, which assembly, which lineage, and what is to happen when two recognised claims to decide conflict directly.
Doctrinal differences can be tolerated for long periods where a recognised procedure exists to handle them. Without an accepted procedure, small differences become unresolvable.
This is why divisions frequently follow political disruption, since the structures that would otherwise settle a dispute lose their reach at the same moment.
Practice divides more visibly than belief
Communities notice differences in calendar, ritual form, dress and the conduct of worship immediately, whereas differences in doctrine require explanation to become apparent.
Because practice is what people share weekly, a change to it affects everyone, while a change in formulation may be noticed only by specialists.
Historical accounts written later tend to emphasise the doctrinal side, partly because those documents were produced by the specialists.
Language and geography harden a split
Once separated communities use different languages, their theological vocabularies drift, and terms translated as equivalents come to carry different implications.
Distance also removes routine contact, so the ordinary corrections of shared life stop operating, and each side develops its account of the other from report rather than from acquaintance.
Positions attributed to an absent opponent are frequently sharper than anything that opponent holds, and the mismatch can persist for centuries.
Reunion works on the same terms
Efforts to heal divisions generally begin with shared practice and mutual recognition rather than with agreement on the formulations that were disputed.
Where progress is made, it often takes the form of acknowledging that different wordings expressed compatible intentions in different languages.
Such processes are slow, frequently stall, and are contested within each community by those who consider the original issues unresolved.
Why divisions persist after the cause fades
Separated communities develop institutions, liturgies, calendars and identities of their own, and these become worth preserving independently of the original dispute.
Reunion then means asking people to give up something valuable in order to resolve a disagreement their ancestors had, which is a difficult proposal.
Understanding that explains why divisions long agreed to be based on misunderstanding can nonetheless remain firmly in place.