Somehow we were sent to invade a nation because it was a direct threat to the American people, or to the world, or harbored terrorists, or was involved in the September 11 attacks, or received weapons-grade uranium from Niger, or had mobile weapons labs, or WMD, or had a need to be liberated, or we needed to establish a democracy, or stop an insurgency, or stop a civil war we created that can't be called a civil war even though it is. Something like that.
It was oil, pure and simple. All the other (attempted) justifications for the war have been proven to be nonsense.
The Iraq war has been a fukup in so many ways.