The fundamental reason for the dynasty cycle is that the elite class breeds more and more over time, and the entire society can no longer support the lower class, even through exploitation. A complete violent reshuffling is necessary to eliminate the old elite class and replace them with a new group of elites. The number of new elites is relatively small, so the lower class can still support them, leading to a period of peace and prosperity. After another two or three hundred years, it will happen again.