Coulda, shoulda, woulda. We don't really have any way at all of knowing, or even supposing, what would have happened, but my inclination would be to believe that a pre-9/11 invasion wouldn't have had any effect on the events of 9/11. A year prior the hijackers were in Germany or the United States. The money for the operation had already been transfered, the planning was already largely completed, the surveilence had already been done. Maybe some intelligence that could have tipped off investigators to the planes operation might have been found in a cave somewhere. Maybe we would have actually gotten bin Laden and disrupted alQ enough that they called off or postponed the attack. Maybe any number of things could have happened. But there's no way to say how it would have shaken out. ETA: Understand that I have no issues with the invasion as it occured, or with a pre-9/11 invasion for that matter. I think that going in there was the absolute right thing to do. What I take issue with is nation building and/or pprotracted "stabilization" campaigns.