Afghanistan was a base of operations for terrorists. Now you can define that a lot of ways, and countries and police forces do define it however is convenient a

Afghanistan was a base of operations for terrorists. Now you can define that a lot of ways, and countries and police forces do define it however is convenient at the time. What matters for this however, is that it was a state sponsor and safe haven for people who'd go random places and blow economic interests up (from planes to tourist locations), located in a place where they actually had a shot at making stuff happen (ie. could have easy access to a lot of places). So Afghanistan had to go, both for it itself having to go, and to serve as a warning to other states what happens if you don't cooperate in the war on terror. The war on terror, of course, being the war to keep congress' economic interests safe.