In Iraq, what matters is not for the war to succeed, but to win the peace.
But the US has a poor record on that.
How come winning is so important? It's not possible all the time and this way of thinking can be conterproductive! Because in a war, there are allies you need and often, later on, those allies are going to become your enemies....The Russians during WW2, the Taliban during the cold war, the Iraqis during their war against Iran...
Clearly, war is not a solution because there is nothing worse. And as long as the peace is not won, another conflict looms, a conflict that will again not be settled as long as the peace is not won.