A central premise of international humanitarian law (IHL) is that the same rules apply to both parties in an armed conflict “regardless of the type of war they fight, the justness of their respective causes, or the disparities in power and capabilities between them.” In her essay, On a Differential Law of War, Gabriella Blum questions that premise, asking whether holding powerful parties to higher standards of IHL compliance than weaker parties might better maximize humanitarian welfare in conflict situations. Her answer is that the humanitarian effect of such “common-but-differentiated responsibilities” (CDRs)—a term she borrows from international environmental law (IEL) and international trade law (ITL)—is indeterminate because it depends on the nature of the CDR, the type of conflict, and whether the weaker party is a state or nonstate actor.
Blum’s normative analysis of the desirability of CDRs in IHL is exceptionally powerful, and I agree with most of her conclusions. This brief response, therefore, is intended to be more constructive than critical. In particular, I want to raise five issues that I believe warrant further exploration: (1) whether permitting judges to differentially apply IHL standards could be seen as legitimate; (2) whether proportionality is the kind of standard that permits differential application; (3) whether, and to what extent, CDRs would encourage states and nonstate actors to comply with IHL; (4) whether the case for CDRs might be stronger in non-international armed conflict (NIAC) than in international armed conflict (IAC); and (5) whether it is possible to assess the humanitarian effect of CDRs without abandoning the jus ad bellum/jus in bello distinction. I conclude that, in fact, Blum’s own analysis supports recognizing at least one kind of CDR: namely, requiring strong states to spend more money than weak states on procuring and using precision weaponry. . . .