Rome was destroyed by inefficient monetary and fiscal policy and an excessive reliance on coercion. The various distinct cultural/national identities across a wide geographic region determined where the splits would be. The splits themselves were from Rome losing its ability to fund things and to influence culture and maintain legitimacy in the eyes of the people.

If a large portion of people (not 100% but most) starts to recognize that every single individual has their own identity and yet they are worthy of respect, a libertarian or anarchic split occurs, where there may be broad national identities but there will be little to no coercion mandating collective action, and instead collective actions become voluntary contributions. This has happened in the past in many places, and it will happen again. There is little stopping it besides silly mystical notions of divine right to rule. That is the basic way the causality works, in rough language. The loss of legitimacy in the eyes of the people.