Why we are at war is really very simple.
You see,in 1991 Iraq invaded Kuwait.The UN then sent forces in to kick him out,which they did in short order.
Since he was a bad boy for doing this and couldn't be trusted to play with dangerous toys,sanctions were imposed.The no-fly zone,no wmd,no missiles that can travel farther than 150km,weapon inspectors,etc.Sanctions he has repeatedly violated(like the shell game he continually played with the inspectors).
Who are we to impose such sanctions?What right do we have to do so?That's also simple.
You see,the side that WINS the war gets to dictate terms to the side that lost.
The twelve years of repeated violations ALONE were enough justification.Add to that the rape camps,the torture camps,shooting at U.S. fighters enforcing the no fly zone,hundreds of thousands of people starving,many because the money from the Oil For Food Program was being was being diverted to the Iraqi military and Hussein's pockets,and last but not least his ties to terrorists groups.
He had his chance to play nice,and he blew it.
That's why we are at war.