Why is Bush attacking Iraq?

Just why is Bush planning to attack Iraq?
If he has real evidence that Saddam Hussain conspired with the Al Qaida, then all he has to do is state that evidence clearly and coherently. Then he doesn’t need the world’s permission to attack, any more than we needed UN permission to defend ourselves when Pakistan invaded us in Kargil.
Instead, the American government drops dark hints laced with innuendo to that effect. When challenged about terrorism, it shifts base and talks about nuclear weapons. If someone asks why America is specifically concerned about Iraq on this score(as against North Korea, India or Pakistan), it points to Saddam Hussain’s record as a tyrant and hints that he is unhinged and capable of anything. It hastens to tell its citizens that asking the UN’s permission is purely symbolic, and hopes that the rest of the world is not listening.
Now, I don’t defend Saddam. If Americans can attack Iraq and replace that tyrant with a half-decent alternative, and do so with as little bloodshed on both sides as can be reasonably expected, Iraqis would be grateful, and so should the world.
Americans are capable of it and have ocassionally done such things, but their overall foreign policy record resembles the history of Mongols’ European invasion.
They have a long history of creating a mess and leaving it for the next President to solve.