The risk that the war in Ukraine escalates past the nuclear threshold

TO A 16TH-CENTURY siege warrior, the art of the escalade lay in climbing up a city’s fortifications without encountering something unpleasantly hot or sharp. To the men who rewrote the rules of strategy for the nuclear age, the art of escalation was the process which, bit by bit, moved a limited war towards an unlimited one. As in sieges of old, the key was a ladder: a conceptual one where each rung both increased the level of the conflict and sent a signal to the other side.

Herman Kahn, one of several inspirations for the title character of Stanley Kubrick’s unmatched treatise on deterrence, “Dr Strangelove”, devised a 44-rung escalation ladder with which to study and analyse the phenomenon. The step from rung nine (“Dramatic military confrontations”) to ten (“Provocative Breaking Off of Diplomatic Relations”), he noted, was the one which marked the point at which nuclear war ceased to be unthinkable.