To me it seems like there is a lot more to this building-flourishing-decay-collapse cycle than power and competence with regression to the mean. I first got interested by this topic after reading "The Fate of Empires" [1] where the author puts the "blame" so to speak, not on competence, but on the generational gap. His thesis is that it takes approximately 10 generations before the values that built the society are no longer followed by their descendants.