Operation Iraqi Freedom
Again: we never really stopped supporting Saddam, we were patting his regime on the back as late as March 2003 ... Even now we're withholding evidence - after the invasion we allowed much of it get looted/burned - regarding many of his crimes, not least because it would implicate US officials.
We invaded in 2003, to be a little presumptious, because sanctions were "eroding", as I recall Powell describing it, and if they eroded sufficiently the regime would have caved in and you'd have either a major failed oil state or more likely a new Iraqi government that, finally free from the bogeyman of our own making and from the mechanisms of control devised after the Gulf War, could act independently of the US.
Iraqi liberation was imminent and we had to prevent that.