The use of force in Iraq in 2003 by the United States, Britain and Australia was justified by these states as an act of self defence, based on the threat posed to them by Iraq’s possession of weapons of mass destruction and its association with terrorists. Other justifications were also raised, including those based on United Nations Security Council Resolutions, and to a much lesser extent those based on humanitarian intervention to assist the people of Iraq remove an oppressive regime. Nevertheless, self defence remained the premier justification, and one which was undermined when occupying troops in Iraq ultimately failed to discover such weapons. That evidence first cited in support of self defence was at best circumstantial raises the question why these arguments were promoted so vigorously, particularly when those based on humanitarian intervention were almost ignored in spite of them having a sound evidentiary foundation. This article argues this course was adopted because acting in self defence will generate support from an electorate to whom elected leaders are answerable and will fit within international law. In contrast, humanitarian intervention, while it also has a legitimate basis under international law, will not promote action from states unless there is some collateral benefit to those states.