The Mandate of Heaven originated during the Zhou dynasty in China, which lasted from 1036 to 236 B.C., and was significant because it was the basis for determining whether the emperor was worthy of ruling the country. This mandate granted the emperor the right to rule, which meant that he no longer was emperor if he lost the mandate.
The Mandate of Heaven consisted of four different principles. According to the first principle, heaven granted the emperor the right to rule. The second principle stated that as there was only one heaven, there could only be one emperor at any time. The third principle was that the emperor's virtue determined whether he was worthy to rule, and the final principle stated that no single dynasty had the right to rule forever.
This last rule was important, as it helped pave the way for the many different dynasties that came into power over time and ensured that the title of emperor couldn't simply be passed down from generation to generation unless all of the rulers were worthy.
If the country was prospering, the emperor was thought to retain the mandate. However, if foreign troops invaded, harvests were bad or there were uprisings, then it was thought that the emperor had lost the Mandate of Heaven.