On my visit to that quarter of Brussels a few years ago, I could see the dangers clearly enough. People like Salah Abdeslam, the terrorist arrested there a few days ago, would swim like a fish in the sea there, to use a Maoist metaphor. Between the sympathetic locals, and the rest of the population—whom they could intimidate into silence—it would be easy for them to hide. This social world is impenetrable to the forces of the state. My informant told me that the Belgian government is unable to collect taxes from businesses there—though it is, apparently, able to distribute social security.

How do you stop ghettos like Molenbeek from forming, and what do you do about them once they have formed? The driver had no doubts: you force the residents to live elsewhere. Conceptually easy. In practice, difficult. The European Court of Human Rights recently ruled against Germany, which sought to do exactly that. Having accepted a million Syrian refugees and immigrants, the Germans wanted to prevent the development of Muslim ghettos by dispersing these immigrants throughout the country. The Court ruled that this was against their fundamental human rights, among which is the right to form several—or many—Molenbeeks.