From Science News: Ancient China: Lack Of Rainfall Could Have Contributed To Social Upheaval And Fall Of Dynasties.

Chinese history is replete with the rise and fall of dynasties, but researchers now have identified a natural phenomenon that may have been the last straw for some of them: a weakening of the summer Asian Monsoons.

Such weakening accompanied the fall of three dynasties and now could be lessening precipitation in northern China. [continue].