Only a few years ago, mass-murder attacks on the West in the name of Islam, like those of September 11, would have seemed like a thriller writer’s fantasy. Nor would anyone have imagined that a bombing by Islamists could swing a general election in a European country, that a Dutch movie-maker might be shot dead on the street for a film about the abuse of women in Islam, or that one might find oneself watching, on television, the beheading of Western hostages by men crying out Allahu Akhbar! over their savage deeds.... At present, it is not clear whether the...