I just finished reading a marvelous collection of essays by Theodore Dalrymple, "Our Culture, What's Left of It: The Mandarins and the Masses". It includes an essay, "Barbarians at the Gates of Paris" in which he describes how the French built these massive housing projects for foreign workers beginning in the sixties, called cites. They've basically evolved into mini Falujas, ringing the city.Yes, this "unassimilated" nonsense was one of the worst things the French ( and many others countries ) could have done.
The Barbarians are, indeed, inside the Gates.