One thing that comes to mind is the old cliche “If all you’ve got is a hammer, every problem looks like a nail.”
The U.S. has a superb military manned by brave competent men and women equipped with awesome tech. Unfortunately our diplomatic and intelligence skills have been faltering, and our counter-terror abilities were all but non-existent prior to 9/11 and have not improved much since.
After 9/11 there was a lot of talk in the air about how we were in a new paradigm. 9/11 was an act of war and we must respond militarily. The old “law-enforcement” paradigm hadn’t worked, and the new “war” paradigm was what was needed. You heard a lot of this from various conservative commentators, such as Charles Krauthammer and the late Micheal Kelly.
The problem is that there really isn’t that much the military can do against Al Qaeda, or any other terror group. The only role it had was the Afghan invasion. Once the Taliban was destroyed, it was just down to some difficult, dreary nation-building. (Although I think we let an opportunity slip by in Tora Bora.) After Afghanistan, what could we do? The only real task would have been to pursue AQ and Taliban fighters into Pakistan, but this was politically impossible, for various reasons. (At least on a large scale.)
So once the Afghan war ceased major operations, there really wasn’t anything for the military to do. Counter-terror would return to the realm of law-enforcement, diplomacy, and intelligence. The conservative commentators were simply, and obviously wrong. There is no real war on terror. The military would serve a vital role in going after AQ supporting states, but the only real one was Afghanistan, and we already did that. AQ is a loosely ordered criminal gang, not a nation that can be attacked and defeated in battle.
So we had to keep the war paradigm going. Where to attack? North Korea has Nukes, Iran is mountainous and huge, Pakistan is our ally more or less, so that leaves Iraq.
In short one of the motives in attacking Iraq, IMO, was simply to keep the military part of the War on Terror going, because that’s what we know how to do.