The growing ability of the US to kill with impunity in war has prompted some to question whether such advantage challenges the moral justifications for inter-combatant violence. This scholarship, however, has yet to properly clarify both the explicit and tacit role of reciprocal risk within this moral determination. A systematic explanation is needed of the function of risk in the right to kill in war. This article engages with the in bello component of the Just War Tradition to determine: first, the role of reciprocal risk in the moral justifications for killing in war; and, second, the extent to which these justifications may be challenged within conditions of radical asymmetry, exemplified today by the unmanned aerial vehicle exclusive violence of the US. The first three sections of this article each review an account of Just War: conventionalism, revisionism and contractarianism. It is argued that the coherence of each of these moral accounts, particularly in terms of the permissiveness of inter-combatant violence, is grounded in an assumption of collective reciprocal risk. Radically asymmetric conditions of battle render ambiguous what would otherwise be a morally unproblematic use of military violence. This article will conclude by highlighting how this challenge manifests in practice, through analysis of the ongoing unmanned aerial vehicle exclusive violence of the US. The radical differentials of physical risk that characterise this violence threaten to erode the capacity of the US to interpret and apply standard judgements of Just War theory against those it targets.
