The French city of Marseillaise has an estimated 30 to 40 percent Muslim population and has been ranked as the most dangerous city in Europe. The gritty Mediterranean port, France’s second-largest city, was appointed the “cultural capital of Europe,” a rotating European Union honor. City fathers launched beautification projects, created new tourism attractions and invited people from around the world to visit. A splendid stone esplanade was laid around the Old Port, peppered with novel sculpture, and a high-tech historical museum went up next to City Hall. How did that work out? The eruption has refocused attention on Marseille’s...