Farming society has limited productivity and can only feed a limited population. Every dynasty changes, there will be a series of wars, which will cause a large number of layoffs. Therefore, at the beginning of each dynasty, the rulers will implement the policy of recuperation, reduce the burden on farmers and restore the economy. After a period of cultivation, the dynasty will have a prosperous period, which will usher in a rapid population growth. The population has increased, but the social productivity has not been improved accordingly, so the food supply will be insufficient, and some people will become refugees and become hidden dangers threatening the security of the dynasty.
Social contradictions intensified with the rise and fall of dynasties. Class problem is a difficult problem that the whole dynasty will face from beginning to end. There are always some big families who keep annexing farmers' land. In the early days of the dynasty, the power of the gate was relatively weak, and farmers also owned their own land. This day can go on. But at a certain time, the Matthew effect will appear in society, the gate valve will become stronger and stronger, and the farmers will become weaker and weaker. In the end, farmers' land will be annexed by the gate valve. Farmers who lost their land either died or rebelled, so peasant uprisings occurred in the late period of almost every dynasty, and then the old dynasty was destroyed in the war and the new dynasty rose.
In short, there are deep-seated reasons behind the replacement of feudal dynasties. When we study the rise and fall of dynasties, we should look at the essence through phenomena.