Not only did it work. It worked magnificently.
Not only did it fail, it failed spectacularly. Here is why.
The military victory our forces achieved in Iraq is unprecedented in the history of warfare with regard to invading a hostile nation guarded by an entrenched defense with numerically superior forces. The insurgency we are now fighting is an entirely different battle.
Simply put, Iraq is not secured. What you have stated above is an example of the phrase, "If the only tool you have is a hammer, everything looks like a nail." Yes, we brought the big hammer, and smashed Saddam's army magnificently. Nailed 'em. Unfortunately, just because we're good at something doesn't mean that it's all we need. The Army doesn't like counterinsurgencies. It likes fighting other tanks and troops. It's good at it. After Vietnam, it got out of the counterinsurgency business to focus on core competency; killing other maneuver units.
That's great, and against the Soviets, a solid decision. The only problem is that our current enemies don't form maneuver units, and don't need to. They don't play our game. It's like trying to hit nails made of soft rubber into a board, but we keep on hammering, because it's all we know how to do.
Your argument is that since the enemy has failed to field a maneuver force that can beat ours, we win. Rules like that are an obtuse vanity we hold ourselves to, but our happily enemies ignore. Victory is determined by who exercises political their will on the other, regardless of how they get it done. We need a force that's capable of doing so, and we need to rethink how we score our games.
And if history proves anything, it proves you cannot defeat an insurgency by trying to overwhelm it with superior numbers of conventional forces.
You can't hammer it down, if that's what you're implying, but more conventional forces coupled with smart policies, cultural awareness and SOF tactics can work wonders.
What was the objective given to Rumsfeld and the DoD prior to the invasion of Iraq? Their objective was to defeat the Iraqi Army and overthrow Saddam. They accomplished both of those objectives in record time with unprecedented success. The Iraqi military ceased to exist and Saddam was found in a rat hole and is currently sentenced to death. There can be no debate on those points. The mission was accomplished.
Flash forward three years. The enemy we are currently fighting is not the enemy we destroyed. That point seems to be lost on the American public. We currently find ourselves fighting an insurgency that has proven itself far more effective in its ability to manipulate world media and opinion than its ability successfully attack our military. Iraq is not secure because it sits right in the middle of a cesspool of terrorist states whose primary focus right now is to humiliate the United States. In all likelihood, we would be faced with this problem regardless of how many troops we employed in our initial invasion or the period afterward. I'm currently sitting in a hotel in Oakland. In this large American city, there are neighborhoods where cops won't go. Yet, somehow, we expect one of the most volatile regions of the world to look like Geneva, Switzerland. It isn't going to happen quickly, no matter how many troops we pour into Iraq. The French proved that in Vietnam and we later confirmed it for them. The Soviet's proved it again in Afghanistan and have continued to prove it in Chechnya. And if we'd like, we can prove it again in Iraq. Hopefully, we won't take that path because it is a sure loser. To defeat an insurgency you have to change the environment and culture in which they operate. And again, as we proved in Vietnam and the Soviets proved in Afghanistan, that doesn't mean bombing the countryside into talcum powder. It takes time, money, patience and the will to win. We can do it if we want. But far too many of our politicians and media wonks have too much invested in our failure. And as of 7 November 2006, they are the side that is currently winning.