Why? Well, the last Shang emperor is reported to have roasted and eaten his opponents, which, you know, bit of a deal breaker, as far as the Mandate of Heaven is concerned. Of course, that might not actually have happened, but it would explain why heaven would allow the Zhou to come to power. So basically, the fact that one dynasty falls and is replaced by another in a cycle that lasts for 3,000 years is explained in the eyes of early Chinese historians by divine intervention based on whether the ruler behaves in a proper, upright manner. It's after-the-fact analysis that has the virtue of being completely impossible to disprove, as well as offering a tidy explanation for some very messy political history. And even more importantly, it reinforces a vision of moral behavior that is a cornerstone of Confucianism, which I will get to momentarily. But first, let's see an example of the Mandate of Heaven in action.