Here is what I think about the reason for the war.
Bush and Co. decided that, after 9/11, America would have a much more proactive attitude toward threats against it. This was part of the whole neo-con active foreign policy idea. 9/11 was a bitter pill to take for America, and they decided, you know, "never again", no matter what it takes. So they invented the Homeland Security Department, started wiretapping without warrants, installing metal detectors in places metal detectors had never been before, and confiscating tubes of toothpaste and nail clippers from airline passengers. And they started invading countries that they felt posed a threat to America. Boom, they invaded Afghanistan. Afghanistan was a training ground for terrorists, terrorists had attacked America. This was not a proportional response to the 9/11 attacks, and it was executed in a way that pretty much guaranteed they wouldn't find Osama, but they did manage to take over the country pretty effectively. Threat to America over. So they start looking for other places that might pose a threat. Bush comes out with the whole Axis of Evil* idea. They start taking a harder line with these countries, and presumably the intelligence agencies are directed to look for information which could indicate any threats to America. Of course, they find some. There are indications that nuclear material has been moved to Iraq. Possible threat to America detected, in, you know, an evil country. America makes the case for war. This time international support is limited, because nobody in Iraq has done anything to America. But that is no longer the criteria, for the American government. Now there just has to be a perceived threat, and it's their policy to go in and end that threat, because, like I said before, "never again".
Bam, they take over Iraq. It was a cakewalk, for the American military. Casualties were (wiki) 172 Coalition soldiers vs. 9,200 Iraqi combatants. That is about a 53:1 kill ratio. Threat to America over.
This is all repetitive, I'm sure you've heard it before. The key point I'm trying to make is that there was this perceived threat, a combination of WMDs and terrorists and a terrible dictator, and in a pretty well unprecedented way Bush just went to war to end it. I mean, there had been American military actions before, but they were generally things like retaliatory cruise missile strikes or direct responses to forces that were doing Bad Things. Complete occupation of a country, without an actual provocation? In the post 9/11 world, that's how America is going to roll.
Now, one wonders what they thought they were going to do once they controlled both of these countries. Presumably they thought they'd install a democratic and/or more importantly US-friendly government, as per usual when the US interferes in other country's governments, and then get out. That didn't work out so well. Paul Wolfowitz(who basically invented the policy I'm talking about here) has admitted that they were wrong about what would happen after the occupation. American soldiers have been in Iraq for five years because once they got there, they didn't know what to do. They weren't exactly greeted as liberators, and the population didn't just roll over and capitulate.
*the Axis of Evil being composed of two countries that fought a decade long war which included the use of chemical weapons and that had dramatic political and religious differences (Iran and Iraq) and North Korea, which of course is not religious at all and doesn't have anything to do with Islamic terrorism or have a lot of political alliances with anybody, let alone Iran/Iraq. What the hell does that even mean?
The drinking will continue until morale improves.