When the United States was attacked on September 11, 2001, its position in the world seemed completely unassailable. Having seen off the Soviet Union ten years earlier, and having then experienced what can only be viewed as one of the more successful economic decades in its over two hundred year history, America at the start of the new millennium looked to be riding high in an international system where it clearly faced challenges and problems but no serious threat worthy of the name. So powerful did it in fact seem that few could even remember that rather anxious little moment just before the end of the Cold War when writers like Paul Kennedy had been talking earnestly about the republic’s inevitable decline over the longer term. A nation with deficits as large as the United States’, and carrying the imperial burden that it did, simply could not go on running the world’s affairs. There was only one way for it to go - and that, he concluded, was downwards.