There are conflicting views as to whether or not this would be a 'resumption of hostilities' and as to whether there is a need for a new resolution. Certainly the UN doesn't see it in the cut and dried way that you guys do. Nor do the governments of Germany and France, who presumably have access to specialists in international law.....
While the USA is not the 'Great Satan' that its enemies claim, and while it can be proud of a better record than most in following an ethical foreign policy usually based on what it sees as being morally right, it does not always act in a high-minded and altruistic way, and all this empty, posturing rhetoric about 'saving Oppressed Iraqis' and about the 'debt which Europe owes' should be recognised as being just that.