The Harappan civilization dominated the Indus River valley beginning about five thousand years ago, many of its massive cities sprawling at the edges of rivers that still flow through Pakistan and India today. But its culture remains a mystery. Why did it leave behind no representations of great leaders, nor of warfare? Archaeologists have long wondered whether the Harappan civilization could actually have thrived for roughly 2,000 years without any major wars or leadership cults. Obviously people had conflicts, sometimes with deadly results — graves reveal ample skull injuries caused by blows to the head. But there is no evidence...