The Cold War could have been for the United States a relatively normal experience of the enemy but without the costs in blood and extreme paranoia which are typical of fought wars. When the Second World War ended, America was still at the height of mobilization and equipped for several more years of war. Islamic terrorism and the aggressive programmes of the administration of George Bush Jr. made it possible to enter the new millennium filling the enemy-gap of the previous decade. Islamic terrorists are for the moment a military power which is impossible to disarm because the weapon is the lives of each one of them. The military expenditure, and in particular the fact that the United States alone spends almost half of the world total, are the subject of continual debate.