re: I knew I forgot something
-- Bush wants to rule the world.
Add that to the list of possibilities. Also...
-- USA wanted to show that their success in Afghanistan wasn't just luck.
-- USA was taking advantage of momentum from the invasion of Afghanistan. Even if other nations would not help invade Iraq, no one would intervene on Iraq's behalf either. And USA had some or all of the above reasons to conquer Iraq. Iraq was a delicious treat.