People forget that Iraq has a massive stockpile of other weapons they were by treaty not allowed to have. For years, the Iraqis had refused or belayed UN inspectors. The day the invasion began, Iraq starting firing missiles at Kuwait it had spent years insisting it did not have.
I know it's easy to only say "we went to war because of the WMDs" or "we went to war because of the oil" or what-have-you, but there was a hell of a lot more to it - and it was almost assured to happen even before 9/11.