IMO, the US HAD the UN sanction to resolve the problem when the security council refuded to act in accordance with it's own resolution.

The UN didn't refuse to act in accordance with the UN resolution. The UN was acting very much in accordance with the resolution, which stated quite clearly that the goal of the resolution was UN inspections in Iraq, which were proceeding according to plan at the time that the US intervened and stopped them, thus violating the UN resolution. We've been over this before.