there is a large collection of countries in the world that do not want to see us take military action against the likes of Iraq and all other middle eastern countries; if we get attacked we will be forced to defend ourselves.
Those countries that hate us are known collectively as The Rest of The World Besides England and Israel.
I'd say, given the possiblity of a crazy domino effect if we launch a military campaign any more ballsy than what we;re doing already it will force people to choose sides. There is the possibility that many of our shaky allies in the mid-east region will come to the understanding that their oil reserves will not last forever and so will not need to be on America's good side anymore and could collectively launch one hell of a campaign against the West.
It wouldn't be an automatic world war three, but it could quite easily escalate given the amount of NATIONAL PRIDE every country in the world has.