Last week, I published an essay arguing that Israel’s military campaign in Gaza is inflicting disproportionate harm on civilians, and that Israel must either accept a ceasefire or drastically narrow its aims and methods. Needless to say, Israel did not accept a ceasefire, its aims have not changed, and its methods have grown more destructive.

Earlier today, Just Security published a response to my essay, which says that a military campaign can never be rendered disproportionate by the total harm it inflicts on civilians, no matter how great. The response lacks legal substance and warrants only a brief reply.

To recall, the question at hand is not whether the Israeli Defense Forces are violating international humanitarian law by carrying out specific attacks that may be expected to cause harm to civilians that would be excessive in relation to the concrete and direct military advantage anticipated. They are (see here). But the question at hand is whether, on the assumption that Israel’s right of self-defense applies to its military campaign against Hamas, the total harm it is inflicting on civilians would render its campaign as a whole disproportionate under the international law governing the use of armed force. It would.

Under international law, States have a legal right to use armed force in self-defense if an armed attack occurs (or, perhaps, if an armed attack is imminent) but only to the extent necessary and proportionate. The requirements of necessity and proportionality are not defined in the United Nations Charter or any other treaty text, so their content must be identified through an examination of State practice. We must look and see what rules or standards States actually use to guide their conduct, to justify their conduct, and to criticize the conduct of other States. This is why serious scholars of international law study debates in the United Nations Security Council over actual incidents in which States resort to armed force, justify their own conduct, and criticize the conduct of other States. These debates are evidence of which rules States accept as law, and form part of the general practice which makes and sustains these rules as customary international law.

The most important Security Council debates regarding proportionality in self-defense are those regarding Israel’s use of force in Lebanon (2006) and Gaza (2009, 2012, 2014).

My essay began by saying that “[a]t the United Nations Security Council, States from every region of the world condemned Israel’s use of force in Gaza as disproportionate and called for it to end” in 2009 and 2014, citing the relevant debates (here and here). I later cited an article by a leading scholar which documented and analyzed the debates regarding Israel’s use of force in 2006. In that article, Christian Tams finds that “the international community, with few dissenting voices, had come to characterise Israel’s response as disproportionate … largely because of the enormity of the ‘collateral’ damage sustained by and within Lebanon.” A similar study of State reactions to Israel’s campaigns in Gaza in 2009, 2012, and 2014, by Christian Henderson, concludes that “the failure of [] past interventions …. and the amount of civilian deaths and destruction leads to the conclusion that the operations were disproportionate.”

All told, several dozen States from every corner of the world determined that Israel’s use of force as a whole was disproportionate due to the total harm it was inflicting on civilians and called for a ceasefire. Few States defended Israel’s campaigns, and none suggested that total harm to civilians was irrelevant to the proportionality of defensive force.

The author of the response, Charles Kels, does not mention any of this State practice, as though its legal significance is not obvious. The author instead asserts that “the jus ad bellum proportionality requirement limits the magnitude of defensive coercion to what is reasonably necessary to secure the lawful objective.” This is, at best, a partial statement of the law. As I wrote in my essay, “[t]he best evidence that most States reject a purely instrumental conception of proportionality comes from prior Israeli bombardments of Gaza and Lebanon.” The author’s assertion was refuted before it was made.

In support of his assertion, the author relies almost exclusively on the following passage of the United States Department of Defense Law of War Manual:

Proportionality involves a weighing of the contemplated actions with the justification for taking action. For example, the proportionality of the measures taken in self-defense is to be judged according to the nature of the threat being addressed. Force may be used in self defense, but only to the extent that it is required to repel the armed attack and to restore the security of the party attacked. As an illustration, assessing the proportionality of measures taken in self-defense may involve considerations of whether an actual or imminent attack is part of an ongoing pattern of attacks or what force is reasonably necessary to discourage future armed attacks or threats thereof.

This is exceedingly weak evidence for a very strong claim. The DoD manual “represents the legal views of the Department of Defense. … [T]his manual does not necessarily reflect the views of any other department or agency of the U.S. Government or the views of the U.S. Government as a whole.” Moreover, nothing in the quoted passage denies that total harm to civilians can render the use of defensive force disproportionate. The first sentence is most naturally read to reject a purely instrumental conception of proportionality. Identifying the force necessary to secure a lawful objective may involve tailoring, but it does not involve weighing in any meaningful sense of the term. Weighing naturally suggests balancing competing values—like the harm an action will inflict and the benefit it will secure—such that either value may defeat the other in any given case. The second sentence does not cut one way or the other. The third sentence states a necessary condition for proportionate force (“but only to the extent”) and not a sufficient condition for proportionate force. It does not exclude the possibility that defensive force must be neither unnecessary in its extent nor disproportionate in its effects. The final sentence identifies potentially relevant considerations but does not exclude others. All told, this inconclusive passage from one department of one State does not provide a substantial legal basis for the author’s assertion which, again, is contradicted by widespread and representative State practice.

My interpretation of State practice is hardly novel. The best recent book on the subject finds, on the basis of an even more extensive study of State practice, that “[c]ivilian harm appears from state practice to be the most important indicator of excessiveness,” (124) “it is uncontroversial that civilian casualties resulting from defensive action are fundamental to considerations of proportionality” (139), and “[f]or states appraising the proportionality of claims of self-defence, collateral civilian harm … acts as a consistent indicator of excessiveness” (145). The book’s author, Chris O’Meara, concludes: “State reactions confirm that a defensive purpose cannot be achieved at any cost. Other interests, in this case of civilians, must be accounted for” (145). This State practice is both widespread and representative, as well as consistent over time, and suffices to establish that total harm to civilians can render defensive force disproportionate under customary international law in some circumstances.

Many legitimate questions remain, but the author raises none of them. As I wrote, we may ask how to aggregate total civilian harm and then weigh it against defensive benefit. We may ask whether total civilian harm can render any use of defensive force disproportionate, or only defensive force that goes beyond halting and repelling an ongoing armed attack and seeks to totally eliminate the military capability of the adversary. We may even ask whether total civilian harm is an independent element of the proportionality requirement (as I believe) or whether it can be incorporated into others (as some suggest). I will leave these questions for another day.

A few odds and ends. When the author first asserts his version of the proportionality requirement, he cites the International Court of Justice’s merits judgment in Military and Paramilitary Activities in and against Nicaragua (Nicaragua v. United States of America). That judgment does not say anything like what the author asserts. The ICJ has never adopted a purely instrumental conception of proportionality. Indeed, serious proponents of the instrumental conception argue against the ICJ’s jurisprudence.

At one point, I cited a report by the Use of Force Committee of the International Law Association for the proposition that “the proportionality assessment should … assess[] whether the harmful effects of the force taken in self-defence are outweighed by achieving the legitimate aims.” The committee members are indeed “impeccably credentialed,” as the author says. And their writings are a subsidiary means for the determination of rules of international law. But I cited the report mainly as a convenient formulation of the legal standard established by State practice.

The author claims that the purpose or function of the proportionality requirement is not to protect civilians, but to uphold the general prohibition on the use of force, and “act as guardrails against an open-ended self-defense loophole to wage aggressive or unprovoked war.” I have no objection to purposive arguments, and this purpose is a good one. But the purpose of the prohibition on the use of force is also to “to save succeeding generations from the scourge of war, which … has brought untold sorrow to mankind.” As Tom Dannenbaum explains, the very categories of “force” and “armed attack” on which this whole body of law turns are defined in terms of loss of life, injury, and damage to property. To say that the international law of armed force is indifferent to human suffering is to miss everything that brought this body of law into being and makes it worth upholding now. And it is to ignore the actual practice of States.

States make international law, for better or worse. States made good law not long ago, in response to terrible human suffering, including in Gaza. They should apply it now, before it is too late.

IMAGE: Members of the United Nations Security Council listen as Israeli Ambassador Gilad Erdan speaks on the Israel-Hamas war at U.N. headquarters on October 30, 2023 in New York City. (Photo by Michael M. Santiago/Getty Images)