When the United States recently announced its commitment to enforce a ‘no-fly zone’ in Libya, the State Department spokesman was asked whether the United States was now at war. He could only manage a floundering non-answer. The unfortunate spokesman’s difficulty with this apparently simple question is a reminder of the vast changes in the nature of military conflict in recent decades. Major conflicts are seldom a matter of one state formally declaring war on another, with a largely agreed set of rules on the conduct of operations (sometimes flouted in horrific ways) and with some generally accepted markers of victory and defeat.