When Saudi rulers send warplanes on missions against Islamic State, they’re targeting a group whose theocratic ideology and roots in desert warfare overlap at least partly with the kingdom’s own present and past. The world’s largest oil exporter has evolved into a mostly urban society in its eight decades of statehood, yet nomadic fighters erupting from the desert in a blaze of religious zeal are still part of its foundation narrative. Today in Saudi Arabia , as in the territory controlled by Islamic State in Syria and Iraq , women must wear black abayas, shops all close during prayer times, religious police enforce Islamic laws and criminals face violent punishment. Saudi Arabia, like its longtime U.S. ally, sees Islamic State as a terrorist group and has joined the war against it. Yet the jihadists share some common ground with their Saudi opponents, even if that’s outweighed by their differences, […]