What would the world look like if we defeated Isis?

The purpose of war is to give yourself a strong position at a peace conference. In the days when warfare was state versus state, that is what generals used to remind politicians: we can bring the enemy to its knees, but it is you who has to design the peace. Sometime between 1991 and 2003, the US forgot this principle and the result is the situation we have now.

Iraq is effectively dismembered into Shi’a, Kurdish and Isis-run territories. Parts of Afghanistan are being reconquered by the Taliban. Syria’s disintegration has propelled millions of refugees into Europe, Turkey and Lebanon. And the Islamic-fascist regime of Isis has staged the first sophisticated “maurading attack” on European soil, killing people who had assumed, like the rest of us, that the disintegration of the Middle East was somebody else’s problem.

Now it is Nato’s problem. In British security circles, there is tacit acceptance that, if it wanted to, France could invoke Article 5 of the North Atlantic treaty, which requires Britain to render military support to an ally under attack. Article 5 is the political deterrent designed into Nato at conception. It gives all signatories the right to wage war legally, as an act of self defence, under principles recognised by the UN charter. It has only once been invoked: by the US after 9/11.