robot warriors lower the barriers to warfare, potentially making nations more trigger-happy and leading to a new technological arms race.

“Wars will be started very easily and with minimal costs” as automation increases, predicted Wendell Wallach, a scholar at the Yale Interdisciplinary Center for Bioethics and chairman of its technology and ethics study group.

Civilians will be at greater risk, people in Mr. Wallach’s camp argue, because of the challenges in distinguishing between fighters and innocent bystanders. That job is maddeningly difficult for human beings on the ground. It only becomes more difficult when a device is remotely operated.

This problem has already arisen with Predator aircraft, which find their targets with the aid of soldiers on the ground but are operated from the United States. Because civilians in Iraq and Afghanistan have died as a result of collateral damage or mistaken identities, Predators have generated international opposition and prompted accusations of war crimes.