In March 2020, on a Libyan battlefield, civilization may have crossed an ominous threshold. Turkish-made autonomous drones reportedly “hunted down and . . . engaged” retreating forces loyal to General Khalifa Haftar with no human guidance. According to a UN-commissioned report, those lethal autonomous weapons were “programmed to attack targets without requiring data connectivity between the operator and the munition: in effect, a true ‘fire, forget and find’ capability.” That was no theoretical scenario devised by military analysts or ethicists. Nor was it a scene from a Hollywood sci-fi thriller about rogue killer robots. It was a real occurrence, one...