The world’s earliest documented water war happened 4,500 years ago, when the armies of Lagash and Umma, city-states near the junction of the Tigris and Euphrates rivers, battled with spears and chariots after Umma’s king drained an irrigation canal leading from the Tigris. “Enannatum, ruler of Lagash, went into battle,” reads an account carved into an ancient stone cylinder, and “left behind 60 soldiers [dead] on the bank of the canal.”