States rarely declare war. For many international law scholars, just war theorists, and moral philosophers, the declaration of war is a moribund tradition that serves no important purpose. When declarations of war are defended, the argument is situated in the war powers debate about executive authority. In contrast, I argue that declaring war – making conditional and reasoned moral demands – continues to be an important requirement for just wars. States should declare war because states should make explicit (formal) moral demands before fighting. Declaring war is procedurally important because it ensures that a state makes a formal moral case, showing respect to innocent third parties whose interests are affected and providing targets the right to confront their accusers and hear evidence. While not a panacea, requiring declarations is a significant improvement on the ad hoc politics of wartime justification that plagues wars such as Iraq. Further, declarations, as ultimatums, are the only reasonable interpretation of the ‘last resort’ requirement in just war theory. A final section extends the argument to contemporary wars against non-state actors, showing that a politics of recognition underlying declarations of war may prove especially fruitful today.

Following the 9/11 attacks, the US declared a war on terrorism, principally aimed at Al Qaeda. The declaration could be dismissed as a sleight of words were it not for the fact that, for the US and for those it affects, it has real and serious legal consequences. The US claims that its declaration of a war on terror is merely an act of self-defence as in its view, Al Qaeda declared a state of war through the 9/11 attacks and these initiated an armed conflict to which the laws of armed conflict apply. Although the characterization of the war on terror as an armed conflict has been rejected by many authorities, the view that the 9/11 attacks were an armed attack giving rise to the rise of self-defence has been widely accepted.

If the 9/11 attacks are armed attacks giving rise to the right of self-defence but the attacks did not constitute an armed conflict; as an act of war, they would not be subject to the laws of war. This would disconnect jus ad bellum and jus in bello in relation to acts of war. If there is a state of war without there being an armed conflict, this would allow the US to take certain measures in relation to the terrorist threat but would not give it the more extensive liberties associated with an actual wartime situation.