As a teenager, Walid Raad would walk around his hometown with a camera, just trying to make some sense of the world. At a glance, the black-and-white pictures he captured then offer cool, detached views. But he quickly discovered there was only so much sense to be made of war-torn Beirut. One day, walking by a bakery, he snapped a cake displayed in the window. It was decorated with birthday wishes for someone named Hassan. Only later, developing the film at home—his dad had converted the bathroom to a darkroom, encouraging his hobby—did Raad register the date: The cake was for Hassan Nasrallah, then a rising militiaman in the Lebanese Civil War. Raad briefly fantasized about poisoning it. “But I was 15,” he told me, laughing.…