Let us be clear about what is happening. Like the Roman Empire in the early fifth century, Europe has allowed its defenses to crumble. As its wealth has grown, so its military prowess has shrunk, along with its self-belief. It has grown decadent in its shopping malls and sports stadiums. At the same time, it has opened its gates to outsiders who have coveted its wealth without renouncing their ancestral faith.

The distant shock to this weakened edifice has been the Syrian civil war, though it has been a catalyst as much as a direct cause for the great Völkerwanderung of 2015. As before, they have come from all over the imperial periphery — from North Africa, from the Levant, from South Asia — but this time they have come in their millions…

It is conventional to say that the overwhelming majority of Muslims in Europe are not violent, and that is doubtless true. But it is also true that the majority of Muslims in Europe hold views that are not easily reconciled with the principles of our modern liberal democracies, including those novel notions we have about equality between the sexes and tolerance not merely of religious diversity but of nearly all sexual proclivities. And it is thus remarkably easy for a violent minority to acquire their weapons and prepare their assaults on civilization within these avowedly peace-loving communities.