The Myth of Jus ad Bellum–Jus in Bello Purity

In modern international law, the separation of jus ad bellum (the law governing the right to go to war) and jus in bello (the law governing conduct in war) is frequently treated as dogma. For some, this separation is unequivocal, with some going so far as to say jus ad bellum may never “override” jus in bello, even when a State’s only alternative is certain annihilation.

This post argues that although the two bodies of law can and perhaps, in many cases, should be treated separately, the notion that the two must—without exception and whatever the consequences (fiat justicia ruat coelum)—remain absolutely separate, is not just unsettled law, but is legally unsupported.

So-called “Settled Law”

That jus ad bellum and jus in bello are and must remain separate in the most absolute sense is not a “settled” point of law. A more holistic analysis shows the legal footing of such a supreme separation is quite weak.

To start, as nearly every critic of commingling jus ad bellum and jus in bello concedes at some level, the two share some kind of bond. “[A]ny formal adjustment to existing jus in bello rules based on a belligerent’s cause would have dire operational consequences,” wrote two authors, but not before admitting “there are practical challenges to cleanly separating the two bodies of law.” Another author concluded, “While it is clear that the rules of [international humanitarian law (IHL)] may not be overridden by jus ad bellum considerations, we have also seen that certain facts may bear on the interpretation and application of the rules in both bodies of law simultaneously.” And as yet another author observed, “jus ad bellum and jus in bello assessments must be kept separate, so that neither contaminates the other. … [However,] [t]his is not to say that there are not interlinkages and co-dependencies between the two bodies of law… .”

Others have noted—Michael Walzer also said as much in his seminal work, Just and Unjust Wars—a “sliding scale” argument that essentially holds a belligerent’s discretion in prosecuting the war increases commensurate with what’s at stake in the conflict (p. 228–32). As applied to the recent Israel-Hamas conflict, for example, Walzer has doubled down on this line of argument, saying “I think the Israel Defense Force has been trying to adhere to the rules in an environment that probably requires some loosening of the rule.”

Yet Walzer is hardly the first to make this observation. “When a war is fought out for supremacy and when glory is the object of war, it must still not fail to start from the same motives which … [are] the only righteous grounds for going to war,” wrote Cicero in De Officiis (Book 1, § 38). Cicero continues, “But those wars which have glory for their end must be carried on with less bitterness.” Grotius writes in The Law of War and Peace, “[T]he means employed in the pursuit of any object must, in a great degree, derive the complexion of their moral character from the nature of the end to which they lead” (p. 250). And as Vattel observes in The Law of Nations, “The lawfulness of the end does not give us a real right to anything further than barely the means necessary for the attainment of that end. Hence it is that the right to such or such acts of hostility varies according to circumstances” (Ch. VIII, § 137). He later removes all doubt, saying, “What is just and perfectly innocent in war, in one particular situation, is not always so on other occasions. Right goes hand in hand with necessity and the exigency of the case, but never exceeds them.”

Some modern thinkers have gone even further, rejecting virtually any separation between jus ad bellum and jus in bello, and arguing it is impossible for an unjust war to be fought justly. Among the most prominent of these is Jeff McMahan. “Whether people fighting in a war have a just cause makes a great difference to whether their acts of war can satisfy the jus in bello requirement of proportionality,” McMahan writes. “One cannot weigh the bad effects that one would cause against the contribution one’s act would make to the end of victory without having some sense of what the good effects of victory would be.”

Another is Thomas Hurka, who writes,

The independence of in bello considerations is plausible for the discrimination condition as traditionally understood, since, whatever their war aims, both sides can refrain from targeting noncombatants. But it does not fit the in bello conditions about consequences, namely proportionality and necessity. If “military advantage” justifies killing civilians, it does so only because of the further goods such advantage will lead to, and how much it justifies depends on what those goods are. Compelling though it is, this view has the radical implication that no act by soldiers on a side without a just cause can satisfy proportionality: if their acts produce no relevant goods, they can never be just (p. 45).

No Basis in Positive Law

Of course, these are merely philosophical objections; surely the rigors of positive law provide a more concrete answer?

Not quite. Even the most committed legal positivists will not find authority for an absolute separation between jus ad bellum and jus in bello. Most obviously, there is the International Court of Justice (ICJ) 1996 Nuclear Advisory opinion. In that case, the ICJ could not reach “a definitive conclusion as to the legality or illegality of the use of nuclear weapons by a State in an extreme circumstance of self-defence, in which its very survival would be at stake” (emphasis added). There, the court affirmed “the fundamental right of every State to survival,” even as it warned that the use of nuclear weapons should “be compatible with the requirements of the international law applicable in armed conflict, particularly those of the principles and rules of international humanitarian law, as well as with specific obligations under treaties and other undertakings which expressly deal with nuclear weapons.” The International Criminal Tribunal for the former Yugoslavia likewise demurred on the question, adding a caveat to its final report by saying, “The precise linkage between jus ad bellum and jus in bello is not completely resolved.”

Then there are the instances in the text of the law of armed conflict’s (LOAC) cornerstone legal documents where jus ad bellum informs jus in bello. For example, there is the prohibition in Article 54 of Additional Protocol (AP) I against the burning of foodstuffs, except in the case of a State defending its own territory. Then there is AP I’s special carveouts in Article 1 for those “fighting against colonial domination and alien occupation and against racist regimes in the exercise of their right of self-determination.” Why would the “why” of waging war matter in these fights but not in other types of conflict?

As emphatic as some are in their belief that keeping the “why” and the “how” of war totally separate is a cardinal rule of LOAC, the idea has virtually no basis in positive law or State practice.

Of course, that much has not stopped anyone from claiming the opposite. One author summarized as much recently:

The separation between the jus in bello and the jus ad bellum is almost an orthodox article of faith for international lawyers. In his seminal textbook on the conduct of hostilities, Professor Dinstein elevated it to a section heading: “No Connection between the Jus in Bello and the Jus ad Bellum” … This is echoed by others in the field. Professor Marco Sassòli has described the separation as “[p]erhaps the most important principle for IHL” (p. 20). Professor Michael Schmitt has called it a “foundational tenet of international law” (p. 39). The International Committee of the Red Cross (ICRC) has underscored that “jus in bello must remain independent of jus ad bellum.” And the list goes on.

The problem? International law experts agreeing on something does not render that “something” law. None of these sources cite any binding law to support the claim that the distinction between jus ad bellum and jus in bello is absolute. The closest they offer is dicta from the Hostages Case (United States v. List, et al.), which itself cites Oppenheim’s treatise. These are, of course, not binding authorities, and nowhere do they claim there is “no connection” between jus in bello and jus ad bellum, that one has “no normative influence” on the other, or that there is an “absolute separation” between the two.

But what about common Article 1 of the Geneva Conventions (GCs)? Consider also its analog in Article 1(1) of AP I, the Preamble to AP I, providing the GCs and Additional Protocols apply “in all circumstances to all persons who are protected by those instruments, without any adverse distinction based on the nature or origin of the armed conflict or on the causes espoused by or attributed to the Parties to the conflict.” Also consider what one author calls “the nature of IHL obligations” (roughly, that “IHL rules are non-transactional in nature and they establish … duties owed to the entire international community”) and that IHL obligations having jus cogens status cannot be overridden. Yet as the same author concluded, even considering these authorities, “[It is not clear] there is a simple definitive answer that would provide the legal foundations for an impenetrable wall that we sometimes assume to exist in this regard.”

I agree and would go one step further. There is no legal foundation for the so-called “impenetrable wall.” The provisions of positive law above stand for nothing other than the simple idea that a State may not “opt-out” of LOAC compliance simply because it believes it is on the right side of the ad bellum question. Next to providing for belligerent equality (which I’ll address below), it is to say what is obvious to even a person of the commonest sense: the ends do not always justify the means.

Recognizing this rule is a far cry from embracing an obstinate and sweeping refusal to acknowledge the effect ad bellum questions necessarily have on in bello analyses, or the absurd notion that States waging a just war must adhere to an interpretation of LOAC that demands their defeat or national suicide. Let us here recall Judge Fleischhauer’s observation from the ICJ’s Nuclear Weapons advisory opinion that “no legal system is entitled to demand the self-abandonment, the suicide, of one of its subjects. Much can be said, in my view, in favour of the applicability of such a principle in all modern legal systems and consequently also in international law” (p. 87).

As for the jus cogens argument, jus cogens requires reflection in State practice. Yet it is not clear States recognize their obligation to LOAC as an unequivocal, impregnable obligation divorced from their reason for going to war. The ICRC’s databases—both those covering rules and State practice—make no mention whatsoever of any sort of absolute division between jus ad bellum and jus in bello.

The U.S. Department of Defense Law of War Manual, for example, rejects such a notion in several respects. “Although jus in bello rules generally operate independently of whether a side has comported with jus ad bellum in the resort to force, parts of jus ad bellum are relevant to jus in bello” (§ 1.11). The concept of “competent authority,” for example, is relevant to both analyzing the prerogative of using military force (jus ad bellum), but also to whether a person may be considered a “combatant” and is therefore entitled to its attendant privileges.

Consider another example: “the jus ad bellum issue of whether a disputed territory belongs to a State affects whether the [jus in bello] law of belligerent occupation applies to that territory because the law of belligerent occupation only applies to territory that belongs to an enemy State” (§ 3.5.3). Yet another example provides that commanders are permitted to “consider the broader imperatives of winning the war as quickly and efficiently as possible and [are] not restricted to considering only the demands of the specific situation” when determining military necessity (§ 2.2.3.1), which is itself informed by the “object of war” (§ 1.4.1).

Almost instinctively, States think in ways that suggest why they fight matters to how they fight, and that when the strategic ends change, the lawful means—and therefore, a belligerent’s understanding of what constitutes harm “excessive in relation to the concrete and direct military advantage anticipated,” for example—change as well. Winston Churchill certainly saw the link between the means and the ends when, in 1939, he called for Britain to seize control of Norway’s territorial waters, which would violate Norwegian sovereignty, but also deny the Nazis access to a critical supply of iron ore. Churchill said, “We are fighting to re-establish the reign of law and to protect the liberties of small countries. Our defeat would mean an age of barbaric violence, and would be fatal, not only to ourselves, but to the independent life of every small country in Europe” (The Gathering Storm, p. 492).

More recently, NATO’s spokesperson linked jus in bello to jus ad bellum by remarking, “There is always a cost to defeat an evil. … But the cost of failure to defeat a great evil is far higher.” Then-U.S. Defense Secretary Donald Rumsfeld said the same in 2001 while discussing civilian casualties in Afghanistan, observing, “We did not start this war. So understand, responsibility for every single casualty in this war, whether they’re innocent Afghans or innocent Americans, rests at the feet of the al Qaeda and the Taliban.”

Whether one agrees or disagrees with these statements is beside the point; they clearly reflect an understanding that jus ad bellum matters a great deal to jus in bello.

Belligerent Equality

Another answer might be that LOAC’s principle of belligerent equality—the notion that all belligerents are equally bound to comply with LOAC regardless of the conflict’s origins—does the heavy lifting for the separation theory. While this argument may carry weight in some respects (e.g., a State’s status as an aggressor will likely have no bearing on whether the members of its military are entitled to prisoner of war status upon capture in an international armed conflict), in other respects, this distorts the meaning of “equal.” Equality under the law does not demand willful blindness to the circumstances involved in a case, but the opposite. As a matter of fundamental fairness, facts like “who started it” and “what’s at stake” are critically important.

This is hardly a new concept, at least in American law. In New York, for example, all people are equally prohibited from using unreasonable force in self-defense. But whether force is “reasonable” turns decisively on the origin and nature of the threat. Indeed, in the doctrinal case concerning the right to maim or kill in self-defense, United States v. Peterson, the court held that for such deadly uses of force, “[t]he defender must have [reasonably] believed that he was in imminent peril of death or serious bodily harm, and that his response was necessary to save himself therefrom.” Moreover, “one who is the aggressor in a conflict culminating in death cannot invoke the necessities of self-preservation.”

Under the Fifth and Sixth Amendments to the U.S. Constitution, criminal defendants are equally entitled to a series of procedural safeguards, regardless of what crime they may have committed. Yet the facts of each case will affect how these safeguards apply. In a case involving a child victim, for example, a defendant may not be able to directly cross-examine a child witness in the same way as an adult witness. Similarly, where a pickpocket may be released on a recognizance bond pending trial, a serial killer may be held without bail for the public’s safety.

In estate law, executors of a deceased’s estate are equally bound to perform their duties in accordance with the testator’s wishes as expressed in a valid testamentary instrument. Yet where a beneficiary has murdered the testator, the executor’s duties will unfold in a way that is profoundly different from other cases, even in ways that contradict the governing statute’s text.

So it is with LOAC. While all States are equally prohibited, for example, from “[l]aunching an attack which may be expected to cause incidental loss of civilian life, injury to civilians, damage to civilian objects, or a combination thereof, which would be excessive in relation to the concrete and direct military advantage anticipated” under the ICRC’s Customary IHL study Rule 14, whether such incidental harm is “excessive” will naturally turn on the “why” of the fight. The answer will necessarily be more permissive for States engaged in a fight for survival (e.g., Israel fighting against genocide, Ukraine defending against territorial conquest) than for those involved in lower-stakes military operations (e.g., a “nation-building” mission in the Persian Gulf; a civilian protection and peacekeeping mission Libya).

Likewise, in circumstances approaching supreme emergency, what the law means by “feasible precautions” will change when faced with, for example, an enemy that uses civilians as human shields as a matter of course. And terms like “distinction” and “military necessity,” will, depending on the “why” of the fight, mean something different than they did in conflicts of lesser intensity or in which the stakes are lower.

Indeed, reason alone tells us this is true. A commander at any echelon cannot accurately assess whether a particular course of action satisfies military necessity or proportionality unless he or she knows the strategic ends of the campaign. Similarly, whether an attack offers a “concrete and direct military advantage” will depend considerably on why a military is fighting in the first place. Flooding a network of underground tunnels with seawater, for example, will likely not suit a limited hostage rescue mission, but doing the same to deprive entrenched terrorists of the freedom of underground movement will dramatically alter the analysis.

Conclusion

To say that a just cause alone does not exempt a State from complying with LOAC is an eminently reasonable position. But to say there is no linkage whatsoever between jus ad bellum and jus in bello—or more ridiculously, that a State waging a just war must accept its defeat, no matter how catastrophic or depraved the consequences, because LOAC says so—is both logically unsound and lacks any basis in law. As I will discuss in my next post, it is also immoral, having the capacity to yield decidedly un-humanitarian outcomes.

A special thanks to Dr. Coleen Watson and CPT(P) Hyun Cho, both of USMA’s Department of Law and Philosophy, and MAJ Tony Lupo, of the Simon Center for the Professional Military Ethic, for their assistance and enriching conversations, which contributed immeasurably to this post.

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Thomas Wheatley is a captain in the U.S. Army and an editor for Articles of War. He is also an Assistant Professor in the Department of Law at the United States Military Academy, where he teaches U.S. constitutional and military law.

The views expressed are those of the author, and do not necessarily reflect the views or official position of the United States Military Academy, Department of the Army, Department of Defense or its components.

Articles of War is a forum for professionals to share opinions and cultivate ideas. Articles of War does not screen articles to fit a particular editorial agenda, nor endorse or advocate material that is published.

Photo credit: U.S. Army, Capt. Alexander Watkins