Events four years ago in New York, Washington, and Pennsylvania alerted a somnolent world to a campaign against the West which had been growing for decades. From September 11, there was a benchmark. To those who lied that there was no terrorist threat, all one had to do was point to the scars of New York City. To those who lied that reacting to terror causes terror, that city’s violation disproved that claim.

There are still today many people who insist that the jihadist attacks on so many cities—including, now, my home city of London—are not part of some wider campaign. There are, also, legions of paid and unpaid apparatchiks propagating the notion not only that there is no wider campaign, but that any wider campaign has nothing to do with Islam. Such claims—as is becoming clearer with each attack—are based not on knowledge, but on hopefulness, not on truth, but on helplessness. Wester ...