In southwest Israel, at the border of Egypt and the Gaza Strip, there is a small crossing station not far from a kibbutz named Kerem Shalom. A guard tower looms over the flat, scrubby buffer zone. Gaza never extends more than seven miles wide, and the guards in the tower can see the Mediterranean Sea, to the north. The main street in Gaza, Salah El-Deen Road, runs along the entire twenty-five-mile span of the territory, and on a clear night the guards can watch a car make the slow journey from the ruins of the Yasir Arafat International Airport, near the Egyptian border, toward the lights of Gaza City, on the Strip’s northeastern side. Observation balloons hover just outside Gaza, and pilotless drones freely cross its airspace. Israeli patrols tightly enforce a...