| Wars usually end when there is a formal declaration of surrender from one of the engaged powers. Since the old government in Iraq has been mostly arrested and/or killed, one can assume that this isn't going to happen. So you consider the other criteria for winning a war.
The next logical step is to check for pacification of the country you've invaded. If there's no fighting going on (q.v. Germany after WW2) and the threat of an uprising is minimal, you can assume you've won the war. This most definitely is not the case in Iraq. There are factions within the nation that are vying for power and trying to bring as much harm against the invaders as possible.
So now it's a war of attrition. The anti-American Iraqis are putting their zealotry toe-to-toe with American emotional and political endurance.
Guess which one will probably prevail. | 
