Question

The rise and fall of the Chinese dynasties were mostly because of what factor?

Answer 1

Because each one bar the Han dynasty got smashed apart by the previous one. Or fell apart anyways.

Answer 2

Also barbarians.

Answer 3

External invasions and sometimes internal corruptions from emperors
The Mongols and the nomadic Xiongnu tribe invaded China. Also the Mandate of Heaven was ignored and therefor most Chinese thought that ignoring this brought corruption from the emperors and their administration