While I could not possibly compete with the humour of BEagle the quote below may help.
'Aggression in international law is defined as the use of force by one State against another, not legally justified by self-defence or other legally recognised exceptions. The illegality of aggression is perhaps the most fundamental norm of modern international law and its preventin the chief purpose ofthe United Nations. Even before the UN, the League of Nations made the prevention of aggression a core aim; and the post-World War II Allied tribunals regarded aggression as a crime under the rubric of crimes against peace.'
I plagiarised this from a book I had lying around at home. I suppose the essential question may be where the UN stand on any proposed military action against Iraq?
A second good question would be to ask whether or not we would be even considering such a course of action if the US didn't need an ally?