If they had a good enough reason to invade Iraq and Afghanistan prior to 9/11, then why didn't they? I've thought long and hard about this, and I think it all has to do with the slogans.
Before 9/11, if they were to have invaded either country, it would be referred to as "The War Because They Wanted One".
After 9/11, it became the "War On Terror".
It's all about the slogan. You can't have a war without a good slogan.