Answer:
The Mandate of Heaven was created under the Zhou Dynasty. According to the Mandate of Heaven, China could only have one ruler at a time. The one ruler was considered to be the 'son of Heaven' and he was made the ruler with approval of Gods.
If a rule was not fair in his duties, then it was considered that God might have taken back His approval. Also, conditions like famine and natural disasters were considered that the Gods were unhappy with the ruler.