This volume was produced in the context of the crisis of legitimacy that occasioned the 2003 Iraq War. As is well known, a bitter feud broke out in the United Nations Security Council (UNSC) over the legality of using force against Iraq. The US government justified going to war in the context of a new doctrine of preventive use of force for self-defence – a doctrine that was soon named after President George W. Bush. The British government anchored its case for war in two previous UNSC resolutions; res. 678 which originally authorised use of force against Iraq in the 1990-91 Gulf War, and res. 687 which suspended res. 678 on a number of conditions including the disarming of Iraq's weapons of mass destruction (WMD) stockpiles, facilities and programmes. Both the US and British positions were underpinned by intelligence, subsequently proved to be flawed, that Iraq had failed to get rid of its WMD. Opponents of the war disputed this intelligence and, moreover, argued that the Bush Doctrine was plain illegal and ridiculed the British idea of resurrecting twelve-year-old UNSC resolutions.

War is invariably accompanied by debate, if not controversy, over the legitimacy of using force. Whilst formal declarations of war have gone out of fashion, governments (both democratic and dictatorial alike) still justify their military action to home and foreign audiences – even if this requires fabricating manifestly false reasons to legitimate using force. Alongside this longstanding state practice of justifying use of force is the increasing codification of legal rules on the use of force. Indeed, major wars periodically generate crises of confidence in international society about the legitimacy of military force as an instrument of world politics.