That was the official reason given, Amos. I think the real reason was much more along the lines of occupying a vital strategic region that rests across key strategic trade and transport routes to Russia, China, the Middle East, and India (which is why major empires have been fighting over Afghanistan for centuries now)...and which allows direct access to the oil-producing regions in the Caspian...and which enables encirclement of Iran.

Retribution for 911 was just the PR excuse to get the public onside for what is a typical imperial war by a great power with the usual imperial objectives. The Afghans did not plan or carry out the 911 attacks, and I'm sure they were as shocked and astounded as anyone when those attacks occured. Those attacks were the propaganda key that unlocked Pandora's Box, and the Afghans were simply the hapless recipients of the hellstorm that was unleashed. They are very good, though, at fighting invaders. Their history has proven that time and again.