OK the UN had NO resolution in place prohibiting the US from taking unilateral action.

Actually, this is not correct. The very same resolution the US has been using as its justification for the invasion, specifically binds the US as well as all other member nations to honor the sovereignty and borders of the Iraqi nation, and to not interfere in the UN inspectors' ability to do their job. By invading, the US forced the inspectors to leave Iraq, and the invasion was a violation of Iraq's sovereignty and borders. Because of its invasion of Iraq, the US is in violation of the very resolution it has been using to justify the invasion.