The USA decided that Irak wasn't cooperating, and that weapons weren't being found because of deviousness. The UN was asked to do something about it. As time passed and weapons continued not to be found, the USA became impatient, and declared the UN inspections ineffective. There were weapons in Irak that shouldn't be there, they said, and they were going to find them.
The UN mulled over making strong statements of intent, but this wasn't enough for the USA. The USA expected the UN to set a deadline for Irak, by which date it needed to prove it had no weapons. Irak sent some documentation to show it no longer had weapons. The USA declared this to be devious, incomplete, uncooperative, and a lie. Having decided that the UN had failed in its mission, the USA took matters into its own hands. The UN evacuated its personnel from Irak as the USA sent its own troops in. The country had to be invaded and taken over before work on weapons inspections could truly begin. As the problem was assumed to be a lack of cooperation from the national government, it was removed.
To this date, USA forces have yet to find any of the weapons it claimed were to be found. It has not set a deadline for finding such weapons. Month after month, we hear it again: "nothing has been found yet, but we're not done either." With no deadline set, this can continue forever.
Now then, remind me, how is what we're doing any better than what the UN was doing? We haven't found more weapons than the UN did. The difference was this: while the UN was verifying that Irak was complying with sanctions, the USA was looking for a violation it believed to have already happened. "Shoot first, ask questions later" is here the method, rather than "innocent until proven guilty."
It's quite possible the UN inspection teams were being constantly fooled. It's also possible there are banned weapons in Irak, even now. But to push an international organization (of which the USA is a member country) out of the way, and do no better, without even setting a higher standard for ourselves (at least providing a deadline) is just foolish, unfriendly, uncooperative, and generally counter-productive. We really do owe an apology to the UN for being head-strong, proud, arrogant, and terribly wrong. If nothing else, the evidence on which we acted has been shown to be false. Even if weapons are found, it's now practically sheer coincidence.
How could the UN have done better? Should it have told Irak to hand over weapons or face war? What weapons? Should it have told Irak to hand over proof that there were no weapons? What could they have provided that would be satisfactory? The only thing that would show there were no weapons would be to scour the country thoroughly with our own teams, and apparently wasn't enough. But there was another solution, which I suppose we implemented: attack the country, and watch to see if any banned weapons are used. None were. Either they're stupid, or really smart, or just didn't have weapons.
And now we're going to hand the country back over to its people. I wonder if we'll leave without ever really knowing if they had weapons in the first place, and might still have them once the people are in power.
Update: Two years in a row, our top weapon-seekers have reported that nothing has been found, and nothing is likely to be found. We have officially stopped searching. Our leadership maintains they were simply mistaken, their intel flawed, and that they would do it all over again if given the chance. The war may now proceed on entirely different justifications; we are asked to forget we ever had any others.