Whenever you read about the fall of civilizations, frequently succession crises lead to the fall of dynasties, and massive civil wars were frequently nails in the imperial coffin.
Yet for most of Roman Imperial history, there were endless civil wars and usurping of imperial power by random generals.
How did the empire manage to not collapse? Who ran the day to day affairs of the empire? How were regular Roman citizens affected? Was it just centuries of barely hanging on by a thread? Was it centuries of utter chaos, starvation, and war?
I talked about this topic over here. I can answer (maybe) followup questions here, since that thread is archived.