The Mandate of Heaven was an idea that allowed the dynastic cycle to happen.
The Mandate of Heaven influenced the dynasties of China. When a dynasty was in control of China, they had the Mandate of Heaven. The Mandate of Heaven is a Confucian idea that says that the emperor is instated by Heaven. Dynasties could lose the Mandate of Heaven if the emperor was not popular with the people, and could be overthrown and replaced with a new dynasty and emperor who had the Mandate of Heaven. Rivaling dynasties used the Mandate of Heaven as a way to justify the political unrest the rivalries brought.
The Qin dynasty used this as a way to justify their conquering of all the other states when they took over what is now known as China.