Keys provides good evidence that a catastrophic world event, a volcanic eruption in the area of Krakatoa, took place around 535 AD and that it had a significant impact on many cultures.

Keys argues that this event was a trigger that shaped the modern world and even argues that the formation of Kashmir or the modern outlines of the borders between South and Central American countries were determined by these events. Even without considering the details this is a suspect claim. Does it even mean anything to claim that this event was the cause of such things? Can you make meaningful claims about causality that span 1500 years of tumultuous human activity?

BTW I also recommend Simon Winchester’s book Krakatoa: the Day the World Exploded.