In the Eastern Roman Empire of Byzantium, disputes over proper religious beliefs polarized the state for centuries, giving fodder to the fourth-century pagan chronicler Ammianus Marcellinus’ claim that “no wild beasts are as ferocious as Christians are to each other”.
To us the disputes seem ridiculous: should holy images/icons be allowed? Does Jesus have one or more energies, persons, natures? Was Mary the Mother of God or of man? And did Christ use Aristotelian syllogisms in his teachings (for reals – accusation against an 11th century bishop who ended up being condemned).
Sometimes the arguments were merely heated shouting matches, as this illustration about the role of icons depicts. Sometimes the heretics’ reputations suffered. I like how the iconoclast Emperor Constantine V got renamed “Kopronymos” or “he whose name is crap/feces/shit” after he died and his opposition took power. Other times, the consequences were more dire: loss of property, exile, even execution (this was rarer than in European history, though).
The arguments pitted Byzantines against each other and softened the ground for political weakness. For instance, the sports teams the Blues and the Greens divided along religious lines and almost overthrew the government during the Nike riots. Eventually, Byzantium lost some of its wealthiest territories during the seventh-century Islamic invasions — the areas had been religiously divided for a long time.
Source(s): Skylitzis Chronicle, Wikipedia, for image. _A Cabinet of Byzantine Curiosities_, Anthony Kaldellis, pp 136-129., Oxford Uni Press, 2017.