In the Han Dynasty, a cluster of calamities, prodigies, and heavenly omens meant that the emperor had lost the mandate of Heaven. The success or failure of the people was thought to be controlled by the gods, along with who should rule. If an emperor was no longer deemed acceptable, natural disasters or disastrous occurrences were taken, then, that the emperor no longer held the gods' approval. This was reason enough to overthrow or replace him.