Since the collapse of the Russian bloc at the end of the 80s, and the resulting disappearance of the western alliance, the US, the world's only remaining superpower has been permanently forced to take the initiative on the military level, where it enjoys a crushing superiority over all its rivals, with the aim of defending its global leadership from the growing challenge from France, Germany, Russia and China. Since the first Gulf war, all the major conflicts have been the result of a pre-emptive policy by the USA, aimed at forestalling the emergence of a new imperialist bloc. But the US is in the grip of an insoluble contradiction: each new offensive, while it momentarily puts a brake on the challenge to American leadership, at the same time creates the conditions for further challenges, by increasing feelings of frustration and anti-Americanism. The whole escalation since September 2001, which has seen the USA, under the pretext of the struggle against terrorism and 'evil dictators', carrying out the military occupation of Afghanistan and Iraq without the least concern for the role of NATO and the UN, is bound up in this logic. Nevertheless, none of the conflicts which preceded Afghanistan, and above all Iraq, have engendered such a difficult situation as the US is now in.