In one of the most important events in all of Asian history, either the Ming dynasty or the Yuan dynasty seized control of mainland China during the eighth, 12th, or maybe even the third century. "The rise of one of these two dynasties, at the turn of whatever time it was, ushered in a bold new age of either unity, feudal infighting, or perhaps both," said historian Robert Grossman, who has devoted his career to parsing out China's incredibly rich and convoluted history. "Not since the days of the Shang dynasty—unless I happen to be thinking of the Qin dynasty—had China undergone such radical change." According to Grossman, either the Ming or the Yuan dynasty is a perfect example of why the other failed to work.