In Honor of Yoram Dinstein – The Separation Between the Jus in Bello and the Jus ad Bellum

Editors’ note: This post is part of a series to honor Professor Yoram Dinstein, who passed away on Saturday February 10, 2024. These posts recognize Professor Dinstein’s work and the significant contribution his scholarship has made to our understanding of international law.

Even though he sometimes lamented that we live in an era of excessive specialization, Professor Yoram Dinstein was one to resist this trend rather well. His scholarly work spanned many areas of public international law, and it is no understatement to say that he helped shape the broad fields of the law on the use of force (jus ad bellum) and international humanitarian law (IHL, or jus in bello) for decades. It is in honour of this wide-ranging legacy of Professor Dinstein that I decided to offer, in the context of this forum, some thoughts on the relationship between these two bodies of international law.

The topic is an evergreen of the genre that can be traced back to medieval times, and yet one that keeps returning in new garb in ongoing conflicts including the wars in Ukraine and Gaza. Today, rather than focusing on specific contemporary conflicts, I will delve into the foundational issues that underpin the separation between the jus in bello and the jus ad bellum. I aim to explore the legal justification for this distinction, as well as some of its legal consequences. Through a critical analysis of the relevant rules of international law, I seek to uncover the deeper legal reasons that support—or perhaps complicate—the so-called “separation principle.”

Protective, Pragmatic, and Logical: the Separation Principle is “A Good Thing”

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” (p. 5). 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.

On reflection, this is somewhat curious. After all, we do not make such strong claims about any other pairings between IHL and other areas of international law. Whether one thinks of international human rights law, international criminal law, international environmental law, international investment law, or even international space law, the trend has been to recognize co-application and consider how IHL might be affected by (or might affect) those other legal regimes.

What, then, motivates the unique approach to formulating the relationship between the jus ad bellum and the jus in bello? The policy reasons behind the separation principle are well-known and can be grouped into two or three main categories. Chief among them are the humanitarian reasons. In any armed conflict, there are victims on all sides who need and deserve protection, regardless of how the conflict began. Most would agree that it is morally indefensible to allocate legal safeguards for individuals on the basis of a conflict’s origin.

Perhaps as important are the pragmatic concerns. No party to an armed conflict will willingly describe itself as the aggressor. “Are we the baddies?” is a great line in a TV comedy sketch precisely because it involves a degree of self-reflection that we have learned not to expect in real life. From the pragmatic perspective, the separation principle ensures that all conflict parties are held to the same standards of conduct regardless of “who started it.”

One could also add reasons of logic. The jus ad bellum constitutes, in a sense, the primary layer of obligations, applicable in the ordinary circumstances of peace. Conversely, the jus in bello is the secondary layer, which only becomes relevant if that primary layer is violated. From this perspective, logic demands that the secondary layer of rules should apply independently of the primary rules’ application or breach—otherwise their purpose would be defeated.

These reasons are well-known and persuasive. What they help establish is that the separation between the jus in bello and the jus ad bellum is protective, pragmatic, logical; it is a good thing. But these rationales do not provide a legal basis for the division. As we have seen, the generally accepted understanding of the separation principle is that, as a matter of law, jus ad bellum considerations must not affect the application and interpretation of IHL. The three policy reasons simply do not address the legal dimension of the issue.

What is the Legal Basis for the Separation Principle?

When I started writing this post, I was surprised at how little discussion of this question there is out there. Although the separation is considered to be of fundamental importance, most writers (though there are some exceptions) simply assert it, often with reference to the policy reasons discussed earlier, but do not go much deeper into what its legal justification might be.

I acknowledge that not everyone might see the search for such justification as a realistic goal. For instance, Professor Marko Milanovic wrote in 2013 that “the separation principle can only be justified externally, outside the law” (p. 66). However, if this were the case, it would lead to a curious—and perhaps unique—consequence that the relationship between two bodies of international law would be determined not on the basis of legal reasons, but solely on extra-legal considerations.

Writing in the same journal issue, Professor Joseph Weiler and Abby Deshman suggested that the legal basis should rather be located in the “teachings of the most highly qualified publicists of the various nations” in the sense of Article 38(1)(d) of the Statute of the International Court of Justice (ICJ). In other words, the separation principle would be part of international law because scholars of Professor Dinstein’s calibre have said that it is.

Personally, I also do not find this approach entirely convincing. Scholarly publications are only a subsidiary source of international law, which means that—in Professor Hugh Thirlway’s words—they “only carry weight in so far as they refer . . . back to one of the three principal sources” (p. 144). Therefore, it is essential to examine what support (or the lack thereof) these principal sources may offer for the separation principle. I turn to this question in the next section.

Three Legal Challenges to the Separation Principle

There are at least three fundamental rules of international law that appear to be in tension with the separation principle.

First, there is Article 31(3)(c) of the 1969 Vienna Convention on the Law of Treaties (VCLT). This provision prescribes that in the interpretation of international treaties, “any relevant rules of international law applicable in the relations between the parties” must be taken into account. This means, as the ICJ held in the Namibia advisory opinion, that “an international instrument has to be interpreted and applied within the framework of the entire legal system prevailing at the time of the interpretation” (para. 53).

This interpretive approach poses a challenge for the separation principle. After all, there is little doubt that the “entire legal system” comprises both bodies of law. Jus ad bellum rules are certainly “relevant” when it comes to the use of armed force between States. And as rules that are found in the UN Charter and customary international law, they are also applicable in the relations between any two or more States that are parties to an armed conflict. Would it thus be correct to conclude that international law requires IHL (treaty) rules to be interpreted in light of the jus ad bellum?

The second challenge lies in the customary law of State responsibility as reflected in Article 21 of the International Law Commission (ILC)’s Articles on State Responsibility. According to this provision, the use of force in self-defence is a circumstance precluding wrongfulness under general international law. In other words, self-defence may justify the non-performance of obligations under international law provided that such non-performance is related to a lawful measure of self-defence in accordance with the Charter. On the face of it, this again presents a problem for the separation principle. Could it not be argued that, as a matter of law, a State acting in self-defence—i.e., in furtherance of its rights under the jus ad bellum—is absolved of its obligations under IHL?

Third, Article 103 of the UN Charter highlights the primacy of Charter obligations in the system of international law. It prescribes that “[i]n the event of a conflict between the obligations . . . under the present Charter and . . . under any other international agreement, [the] obligations under the present Charter shall prevail.” IHL rules are indeed codified in various “other international agreement[s]” such as the Geneva Conventions and their Additional Protocols. At the same time, the UN Charter sets out the key jus ad bellum obligations. Hence, it would appear that those obligations must also prevail over any conflicting rules of IHL.

At this point, it may be useful to clarify the scope of the problem. Article 103 does not pose an issue with respect to uses of force that are permissible under the Charter framework, like the use of force in self-defence or under the authorization of the UN Security Council. This is because such uses of force are not conducted in pursuance of an “obligation” under the Charter but are rather recognized or authorized by the Charter as exceptions from the general prohibition to use force.

It would also not be an issue with respect to the prohibition against the use of force codified in Article 2(4) of the Charter. True, the prohibition—like any prohibition—also encapsulates an obligation not to violate it, i.e., in this context an obligation not to use force. But it is hard to identify an “obligation” under IHL which would be in conflict with the duty to refrain from resort to force. If States do not use force, there is no armed conflict and thus no need to apply IHL in the first place.

Still, one can imagine conflicts between Charter obligations and the rules of IHL. This could be the case if the UN Security Council passed a binding resolution under Chapter VII of the Charter that would contradict States’ obligations under IHL. For example, it could determine that a belligerent occupation has come to an end even though the facts on the ground would prove otherwise. Would this absolve the Occupying Power of its IHL obligations under the law of occupation on the basis of Article 103 of the Charter?

Three Elements of an Answer

These are all real and practical issues that seem to undermine, or at least question, the supposed wall of separation between the jus in bello and the jus ad bellum. I am not sure that 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. However, I can think of several elements of an answer that addresses the challenges outlined above to some degree (if not fully).

The Nature of IHL Obligations

The first element relates to the nature of obligations under IHL. IHL rules are non-transactional in nature and they establish obligations erga omnes, i.e., duties owed to the entire international community. As such, all States have a legal interest that parties to armed conflicts comply with the rules of IHL. Accordingly, those circumstances precluding wrongfulness which are predicated on bilateral relationships—such as self-defence—are without effect in relation to obligations owed to parties outside such relationships, including obligations under IHL.

This interpretation is corroborated by the fact that many IHL obligations have jus cogens status. This has been recognized by the ICJ, which held in the Nuclear Weapons advisory opinion that “a great many rules of [IHL] . . . constitute intransgressible principles of international customary law” (para. 79). As such, in accordance with Article 26 of the ILC’s Articles on State Responsibility, these rules cannot be overridden by any of the circumstances precluding wrongfulness. Relatedly, it is generally accepted that as rules from which no derogation is permitted, jus cogens norms cannot be overridden by operation of Article 103 of the UN Charter either.

Duty to Respect and Ensure Respect

The second element is found in IHL rules that require States to respect and ensure respect for IHL “in all circumstances.” This is a requirement in relation to the Geneva Conventions, codified in their common Article 1, and thus, given the universal ratification of these treaties, binding on all States. As per Article 1(1) of Additional Protocol I, it also binds all State parties to the Protocol as regards the rules comprised in that instrument. And the ICRC considers it to be an obligation in relation to IHL in general (see also Rules 139 and 144 of the Customary IHL Study; para. 2 of Resolution 1 of the 26th International Conference of the International Red Cross and Red Crescent).

As noted in the ICRC commentary on common Article 1 to the Geneva Conventions, the phrase “in all circumstances” means that as soon as the relevant rules of IHL begin to apply, “no State . . . can offer any valid pretext, legal or other, for not respecting [these rules] in their entirety and in regard to all whom they protect” (para. 219, emphasis added). This means that no legal reasons, such as whether or not the State is acting lawfully under the jus ad bellum, can be relied on as a justification for diverging from what IHL requires.

While certain other aspects of the ICRC’s interpretation of common Article 1 have raised some controversy (for some examples discussed in the U.S. context, see this recent post by Professors Michael Schmitt and Sean Watts), this is not the case in relation to this point. Interestingly, the U.S. Department of Defense’s Law of War Manual makes the exact same observation. At § 3.5.2.1, the Manual endorses the interpretation of the phrase “in all circumstances” as meaning “that a Party’s obligations to respect and to ensure respect for the 1949 Geneva Conventions applies [sic] regardless of whether a Party to the Convention is the aggressor or lawfully using force in self-defense.”

Whether one can extend this logic to the entirety of IHL depends on whether one accepts—as per the ICRC view mentioned earlier—that the scope of the duty to respect and ensure respect extends beyond the Geneva Conventions and Protocol I and covers all of IHL (a topic that is well beyond the scope of this post).

Preamble to Additional Protocol I

Finally, the third element of the answer is that State parties to Additional Protocol I have expressly accepted that “the provisions of the Geneva Conventions of 12 August 1949 and of this Protocol must be fully applied 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.”

Apart from another mention of the phrase “in all circumstances”, the quoted part of the Protocol’s preamble also expressly excludes jus ad bellum considerations such as the nature, origin, or causes of the conflict from having any effect on the application of the IHL rules in the Conventions and the Protocol. For the 174 States that have ratified the Protocol, the separation between those rules and the jus ad bellum is thus an unequivocal legal requirement.

Legal Implications, and Some Practical Examples

I would argue that in combination, the three elements outlined in the previous section provide a legal justification for what is usually called the wall between the jus in bello and the jus ad bellum. It does mean that the rules of IHL may not be overridden by considerations pertaining to the jus ad bellum. As Professors Michael Bothe, Karl Josef Partsch, and Waldemar Solf said in their influential commentary on the Additional Protocols, “[t]he Geneva Conventions and the Protocol . . . are equally valid for both aggressor and aggressed without asking for what reasons or on the basis of what motives one or the other is acting” (p. 31).

This interpretation also provides the foundation for another basic principle of IHL: the principle of equality of belligerents. As Professor Dinstein put it, this principle means that IHL rules apply equally “to all Belligerent Parties, regardless of their respective standing in the eyes of the jus ad bellum” (at p. 5). In this sense, the separation principle and the equality principle are two sides of the same coin. However, the separation principle does not mean that jus ad bellum considerations are fully irrelevant for the interpretation and application of IHL. In order not to prolong this post too much, let me offer just three examples, listed in what might be seen as a slightly ascending order of controversy.

Attribution

In some instances, States may claim that they did not violate the jus ad bellum not because the underlying conduct would not be in breach of the general prohibition of the use of force, but because that conduct was not attributable to the State in question.

This was the case, for example, in March 2014, when Russia initially argued that the so-called “little green men” involved in the armed takeover of Crimea were “in fact members of ‘self-defence groups’ organised by the locals who bought all their uniforms and hardware in a shop.” Later, this justification was abandoned by Russia when President Putin officially acknowledged that at least some of these individuals were Russian soldiers deployed in Crimea to support the local pro-Russian forces.

However, if there was in fact no link between a State and armed groups engaged in armed activities against another State, then its absence would also preclude the responsibility of the former State for any violations of IHL by those units.

Conflict Qualification

A number of questions of jus ad bellum may have an impact on the qualification of a situation under IHL and thus on the existence and extent of IHL obligations. This includes first and foremost the question of to whom a given territory belongs. This is because the law of belligerent occupation—a part of IHL—only applies if a territory is brought under the effective control of a State that is not the recognized sovereign of that territory (see, further, the ICRC’s commentary on common Article 2, section E.3).

Another example is the question of consent. Under the jus ad bellum, the use of force by one State on the territory of another does not amount to a violation of Article 2(4) of the UN Charter if the territorial State provides its consent to such operations. The presence or absence of consent is also relevant for the purposes of IHL. If a State does not provide its valid consent to another State’s armed intervention in its territory, the situation will amount to an international armed conflict between the two States (ICRC, Commentary, para. 293). Likewise, if the occupied State consents to the continued presence of the armed forces of the Occupying Power, this brings about the end of occupation (ICRC, Commentary, para. 340).

Proportionality

Under the jus ad bellum, the State acting in self-defence is limited to do only so much as is necessary and proportionate to the goal of repelling the armed attack against it (for a general overview, see Dr Chris O’Meara’s recent monograph). This defence may sometimes entail more force than that used by the attacker and sometimes less: the example of the Falklands conflict illustrates the former. Under the jus in bello, proportionality requires those who plan or decide on an attack upon a military objective to balance the anticipated military advantage of the attack with the expected incidental civilian harm (see Additional Protocol I, art. 51(5)(b) and art. 57(2)).

A controversial question is whether and if so, to what extent, the need to repel the attack of the aggressor (a consideration under the jus ad bellum) may be included in the calculation of the anticipated military advantage under the jus in bello. I agree in this regard with Marco Sassòli’s position that “the military commander may only take jus in bello advantages into account and not, for example, the liberation of civilians under enemy occupation” (p. 500).

However, the line is not always so easily drawn. It is generally agreed that under IHL, the “advantage sought must contribute to defeating the enemy in the military realm” (see the ICRC and Université Laval’s Proportionality report, p. 16). From the defending State’s perspective, the goal of “defeating the enemy” is just a synonym for the goal of repelling that enemy’s aggression.

Arguably, an attack which achieves that goal, or brings the defending State significantly closer to achieving it, will present an important military advantage to that State. It goes without saying that the attack would still have to comply with all applicable rules on the conduct of hostilities for it to be lawful. And yet, it can be said that the same consideration which determines the lawfulness of defensive action under the jus ad bellum would also constitute a relevant factor under the jus in bello.

Concluding Thoughts

Professor Dinstein’s articulation of there being “No Connection between the Jus in Bello and the Jus ad Bellum” highlights an important aspect of the regulation of the use of force on the international plane. As shown in this post, the separation principle is essential for the effectiveness of IHL and supported by compelling policy prescriptions.

However, as a matter of legal analysis, the separation between these two bodies of international law is less of an impenetrable wall and more of a semi-transparent membrane. While it is clear that the rules of 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.

In closing, I would submit that this is not a flaw but a feature of the complex and interconnected system of international law, in which none of its parts may be fully isolated from the rest. As Professor Dinstein wrote over 40 years ago, international law “is derived not from metaphysical sources but from the actual social need of the members of the international community to coexist” (p. 205). It is no wonder, then, that such a need-based system would have evolved to favour complexity and parallel application of related bodies of law rather than an overly rigid, artificial separation.

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Kubo Mačák is Professor of International Law at the Law School and a member of the Exeter Centre for International Law.

 

 

 

 

Photo credit: U.S. Army, Staff Sgt. Bruce Daddis