1. Disappearance of the Indus Valley Civilization With a culture that stretched from western India to Afghanistan and a population numbering over five million, the ancient Indus Valley people—India's oldest known civilization—were an impressive and apparently sanitary bronze-age bunch. The scale of their baffling and abrupt collapse rivals that of the great Mayan decline. But it wasn't until 1922 that excavations revealed a hygienically-advanced culture which maintained a sophisticated sewage drainage system and immaculate bathrooms. Strangely, there is no archaeological evidence of armies, slaves, social conflicts or other vices prevalent in ancient societies. Even to the very end, it seems,...