[observation]

I see that view as a form of revisionism. Was it ethnic based nationalism, or was it ethnic based nationalism and political ideology and perverse financial incentives and class warfare and... seemingly countless other things.

[zo1]

Perhaps we need to look at it from a meta-perspective then? I'd argue that it was caused by the existence, and ultimate subservience of people to, a state. Large states too, where power was allowed to accumulate, develop and weaponize itself in the form of an army.