The Mandate of Heaven (天命) was a principle used to justify the power of the emperor of China, as well as explaining suitability for the office. According to this belief, heaven bestows its mandate to a just ruler, the Son of Heaven. The Mandate of Heaven depends on the virtue of the emperor; if he does not fulfill his obligations as emperor, then he loses the Mandate and thus the right to be emperor. The Mandate of Heaven would then transfer to whoever would rule best. The fact that a ruler was overthrown was taken by itself as an indication that the ruler had lost the Mandate of Heaven. In addition, it was also common belief that natural disasters such as famine and flood were other signs of heaven’s displeasure with the current ruler, so there would often be revolts following major environmental events as citizens saw these as signs of heaven’s displeasure.
The Mandate of Heaven does not require that a legitimate ruler be of noble birth, and dynasties were often founded by people of common birth (such as the Han dynasty and Ming dynasty). The Mandate of Heaven had no time limitations, depending instead on the just and able performance of the ruler and his heirs. Throughout the history of China, times of poverty and natural disasters were often taken as signs that heaven considered the incumbent ruler unjust and thus in need of replacement.
The concept of the Mandate of Heaven was first used to support the rule of the kings of the Zhou dynasty(1046-256 BCE), and their overthrow of the earlier Shang dynasty(1600-1046 BCE). It was used throughout the history of China to support the rule of the emperors of China, including non-Han ethnic monarchs such as the Qing dynasty. This concept was also applied to nearby countries like Korea and Vietnam. A similar situation prevailed since the establishment of Ahom rule in the Kingdom of Assam of Southeast Asia.
The Mandate of Heaven was a well-accepted and popular idea among the people of China, since it argued for the removal of incompetent or despotic rulers, and provided an incentive for rulers to rule well and justly. The concept was often invoked by philosophers and scholars in ancient China as a way to curtail the abuse of power by the ruler, in a system that otherwise offered few checks to this power.
Chinese historians interpreted a successful revolt as evidence that the Mandate of Heaven had passed. In China, the right of rebellion against an unjust ruler has been a part of political philosophy ever since the Zhou dynasty, and the successful rebellion was interpreted by Chinese historians as evidence that divine approval had passed on to the successive dynasty. The Right of Rebellion is not coded into any official law, rather rebellion is always outlawed and severely punished, but still is a positive right grounded in the Chinese moral system. Often, it is used as a justification for actions to overthrow a previous dynasty after a rebellion has been successful and a new dynastic rule has been established. Since the winner is the one who determines who has obtained the Mandate of Heaven and who has lost it, some Chinese scholars consider it to be a sort of Victor’s justice, best characterized in the popular Chinese saying “The winner becomes king, the loser becomes outlaw” (Chinese: ”成者為王，敗者為寇“).
Due to the above, it is considered that Chinese historical accounts of the fall of a dynasty and the rise of a new one need to be handled with caution, since Chinese traditional historical compiling such accounts would tend to fit their account to the theory, emphasize aspects tending to prove that the old dynasty lost the Mandate of Heaven and the new one gained it, and de-emphasize other aspects.
It was a custom in China for the new dynasty to ennoble and enfeoff a member of the dynasty which they overthrew with a title of nobility and a fief of land so that they could offer sacrifices to their ancestors, in addition to members of other preceding dynasties.
The Republic of China allowed the last Qing Emperor to stay in the Forbidden City and keep his title, treating him as a foreign monarch until 1924. The descendants of Confucius were maintained in the title of Duke Yansheng until 1935 when the title was changed to Sacrificial Official to Confucius (大成至聖先師奉祀官), which remains as a position to this day, currently held by Kung Tsui-chang.
Edited from Wikipedia