Revisiting Application of Jus ad Bellum during an Ongoing International Armed Conflict
The relationship between the existence of an international armed conflict (IAC) and the legality of the use of force under the jus ad bellum (JAB) remains conceptually distinct but practically intertwined. Recent conflicts have brought the practical issues arising from this relationship to the forefront of scholarly debate, particularly in contexts where hostilities have resumed after a period of relative calm. What remains underexplored, is whether and to what extent the continuation of an existing IAC affects the need for a separate JAB analysis.
Focusing on the JAB justification of self-defence under Article 51 UN Charter, this post aims to address this question by examining whether the continuation of an existing IAC alters the need for a separate self-defence JAB analysis on renewed hostilities. This raises two subsidiary issues. First, when does an IAC begin and end? In particular, does an IAC terminate during periods of inactivity and recommence with renewed hostilities? Second, where an IAC is ongoing, to what extent is a self-defence JAB analysis required for uses of force occurring within that conflict? Put differently, what role does JAB play once a conflict is already regulated by jus in bello (JIB)? These questions are addressed in turn below.
The Duration of an IAC under International Law
It is generally accepted that because international humanitarian law (IHL) is protective in nature, the threshold for triggering an IAC is deliberately low and the threshold for concluding an IAC is deliberately high. According to an International Committee of the Red Cross’s (ICRC) updated Commentary to common Article 2 of the Geneva Conventions,
[T]here is no requirement that the use of armed force between the Parties reach a certain level of intensity before it can be said that an armed conflict exists … even minor skirmishes between the armed forces, be they land, air or naval forces, would spark an international armed conflict and lead to the applicability of humanitarian law. Any unconsented-to military operations by one State in the territory of another State should be interpreted as an armed interference in the latter’s sphere of sovereignty and thus may be an international armed conflict under Article 2(1).
Pursuant to Article 6(2) of Geneva Convention (GC IV), and Article 3(b) of Additional Protocol I to the GCs, the application of the GCs ceases “on the general close of military operations.” According to the ICRC, evidence on the general close of military operations “is the only objective criterion to determine that an [IAC] has ended in a general, definitive and effective way.” In this regard, “military operations” may be defined as “movements, manoeuvres and actions of any sort, carried out by the armed forces with a view to combat.” This does not necessarily require the use of armed force. An ICRC Commentary explains,
when belligerent States are no longer involved in hostilities but, for instance, maintain troops on alert, mobilize reservists or undertake military movements on their borders, the absence of ongoing hostilities will generally be a lull or a temporary suspension of armed clashes rather than a stable ceasefire or armistice that can be interpreted as the first stage towards an impending state of peace.
Julia Grignon also notes, for instance, that even
ceasefires, both reflecting a practical approach and being the notion that is today the most commonly used when it comes to reaching an agreement to put an end to hostilities, cannot be the decisive criterion for concluding that an armed conflict has ended. Indeed, they only ‘signal[] an attempt to reach a more comprehensive and permanent settlement of an armed conflict’ and are ‘used with reference to suspension of hostilities.’ (p. 86)
Marko Milanović has likewise concluded that a general close of military operations only occurs when there is “no real likelihood of a resumption in hostilities” (p. 174). Thus “[t]he more complex and prolonged the conflict, the more difficult it will be to precisely identify the point in time when it actually terminates” (Sadler, p. 52-53).
So, what distinguishes a “lull or temporary suspension of armed clashes” from a general close of military operations? The answer is case-specific and may depend in part on the position of the parties themselves.
Taking the current Iran war as an example, during periods of reduced hostilities, statements by the parties suggest that they “maintain[ed] troops on alert.” Iran continued to warn that strikes could resume at any minute. Moreover, its State representatives, such as the intelligence chief of the Iranian Revolutionary Guards Corps, Brigadier General Majid Khademi, issued statements claiming, “The war has not ended. We are in a state of temporary pause” (see also here and here). The official positions of Israel and the United States mirrored these statements. Strikes by and against Iranian-aligned proxies also continued during these periods (see Cohen & Shany). These events suggest that the IAC had not “ended in a general, definitive and effective way” (see also here).
Views on Ad Bellum Analysis in an Ongoing IAC
If there is an ongoing IAC, must the parties to that IAC legally justify renewed strikes following a period of reduced hostilities as an exception to the prohibition on the threat or use of force? Here, opinions amongst scholars vary widely.
First, what will be referred to as the “traditional view” in this post argues that JAB and JIB apply at different times. This view posits that a JAB analysis is required at the first initiation of armed force, but once an IAC is firmly established, the JAB framework ceases to apply. As Laurie Blank notes, “the idea that the jus ad bellum ‘will always operate before the [law of armed conflict] comes into play’ is foundational to the ordinary way in which lawyers analyze and advise, students are instructed, and courts adjudicate on questions relating to the use of force” (p. 280).
Many prominent scholars and experts, including Yoram Dinstein, Marco Sassòli and Geoffrey Corn have advocated for this strict separation between JIB and JAB. Reference may also be made to Robert Ago’s Eighth Report on State Responsibility, in which he observed that the limits inherent in the proportionality requirement of self-defence are “clearly meaningless where the armed attack and the likewise armed resistance to it lead to a state of war between the two countries” (Ago, para. 121). Though the traditional view has lost some traction in academia over the last couple of decades (see e.g., Stahn), it is still considered to be the position grounded in “canonic learning and overwhelming practice” (see Kolb).
Second, debate includes a rejection of the traditional view, referred to in this post as the “rejection theory.” This view is based on the argument that because the threshold for triggering an IAC is low, and because an IAC can theoretically last for eternity even in the absence of active hostilities, it would render the JAB framework practically redundant if it was never re-triggered in the course of an ongoing IAC. Moreover, considering that an IAC may be triggered even without the initial use of force amounting to an armed attack, the traditional view could give rise to an absurd scenario whereby a State, which would otherwise be prevented from responding in self-defence, could nevertheless respond with armed force, purely through the triggering of an IAC.
To prevent such absurd outcomes, proponents of this view, such as Gal Cohen, argue,
while no actual hostilities are taking place, the object and purpose of IHL could easily accommodate additional restraints which are in line with the object and purpose of the prohibition on the use of force to maintain international peace and security and prevent the escalation of [armed conflicts]. However, as the [armed conflict] intensifies to a situation of generalised warfare, the object and purpose of IHL, in particular considerations of military necessity, require an interpretation of JAB rules which is more deferential to the rules of IHL” (p. 380. See also p. 367-68).
In other words, it is the intensity of the ongoing IAC that determines whether it is appropriate for the parties to make a JAB analysis prior to a planned strike or not. In this regard, Professor Milanović has argued that where the initial use of force is “so overwhelming that basically any military response to it would be necessary and proportionate,” such as Russia’s invasion of Ukraine, and an IAC erupts, a JAB analysis would only be required by the original victim State during the IAC “for major escalatory steps” or if the aggressor’s attacks recede (See Milanović’s comments to author).
Christopher Greenwood has similarly argued that “the continuing application of this principle [of self-defence] during a conflict … mean[s] that an initiative which significantly widened the scope of a conflict, for example by extending the fighting into a new area, would be unlawful” (p. 223). However, according to Professor Greenwood, “as the scope and extent of a conflict increases, the range of measures which a state may legitimately take in self-defence broadens, so that in a conflict on the scale of the Second World War it is unlikely that the continuing application of the ius ad bellum would have any real significance.” In other words, JAB continues to apply throughout an IAC, but the requirements inherent in the exercise of self-defence are met by the intensity of the ongoing attacks, rendering a new JAB analysis for each strike redundant in a full-scale war.
Closing Gaps with the Jus Ad Bellum
In this author’s view, the rejection theory appears primarily aimed at closing the unavoidable gaps that arise as a result of the different thresholds inherent in the JAB versus JIB frameworks. But this does not mean that one can simply import JAB into JIB territory, where the frameworks were quite clearly developed for different purposes. Either conclusion (no JAB during JIB; JAB continues to apply during JIB) risks blurring the roles of the two regimes, either by rendering certain rules operationally irrelevant, or by creating legal gaps. But only one of these results is likely to generate real unwanted consequences in operational scenarios.
If JAB does not continue to apply during an ongoing IAC, it could open the door to a number of concerning scenarios, but the likelihood of any of these scenarios materialising in a way that would warrant revisiting the traditional separation between JAB and JIB appears remote. There is, as mentioned above, a hypothetical risk that, because of the different thresholds, an IAC can be deemed to have commenced without the occurrence of an armed attack. Hence, if JAB always operates before JIB comes into play, States may use the fact that an IAC has commenced as a justification for the subsequent use of force, essentially bypassing the JAB analysis stage altogether. Additionally, because an IAC, for the right reasons, is not easy to terminate, there is a hypothetical risk that it carries on forever, with few or no active hostilities, allowing the parties to the conflict to use force against each other, sporadically and at random for eternity, without regard for the prohibition on the use of force or the requirements for the exercise of self-defence under UN Charter Article 51.
However, for these risks to materialise, there is an assumption that the law is the only relevant factor that determines whether a State decides to engage in armed hostilities. In reality, there are several factors involved in a State’s decision to resort or not to resort to armed force (see e.g., J.F.R. Boddens Hosang, p. 74-75). The problem that certain irreconcilable differences between legal frameworks create gaps in the law is not unique to these frameworks, and not every such gap needs to be resolved. As Professor Blank argues (p. 287-88),
Within each body of law, states have negotiated and agreed upon certain rules based on their view of how to achieve those goals. The existence of a gap may, like other ‘[u]nclear rules[,] … reflect States’ judgment that more precise or logically consistent rules would prove legally unmanageable.’ Seeking to fill that gap through interpretation may offer the chance to reduce uncertainty and ambiguity, but in the process can unravel the very law states made and consented to through carefully constructed consensus and negotiation … . The ordinary practice of states also suggests that accepting and navigating the gap is more desirable than attempting to reconcile the difference between the thresholds. In most situations where an international armed conflict is triggered at the low end of the threshold, perhaps because of detention of military personnel or other low-level acts, states are highly reluctant to outwardly identify the situation as an armed conflict and instead seek to deescalate the situation.
If, on the other hand, JAB does continue to apply during an IAC, the resulting problems, and their practical consequences, are more difficult to dismiss.
First, this would transpose the JAB analysis typically performed ex ante at the national political level, to the operational level of discrete strike decisions taken within the military chain of command. In other words, military commanders would be expected, in advance of taking an operational decision to carry out a strike, to engage first with whether the strike constitutes a lawful exercise of their State’s right to self-defence, and only after being satisfied that that is the case, whether the strike is likely to comply with IHL.
That is problematic. As J.F.R. Boddens Hosang notes,
the use of force in the context of national self-defence is a political decision to be made by the national command authorities … it is not up to the individual serviceman, regardless of rank, to determine whether the actions taken by (the agents of) another State require or authorize a response on the basis of national self-defence unless that serviceman was explicitly and clearly authorized to do so by the national command authorities (p. 77).
This is because at the governmental level, it may be assumed that those responsible are aware of the “legal risks related to decisions taken at that level”, whereas “it is not entirely certain whether individual servicemen are aware of the responsibilities and risks inherent in autonomous decisions regarding the use of force in the context of self-defence, especially in the context of complex military operations.” This would place “a significant burden of judgment on the shoulders of the individual serviceman, who may not have recourse to the information required to make an educated evaluation of the merits and risks involved” (p. 75).
Second, with JAB taking on the role of governing both the initial resort to inter-State force, as well as the operational execution of force within an IAC, the permissive clauses of IHL, such as the right to direct attacks against military objectives, or the principle of military necessity—with necessity being linked to achieving the “known military purpose” of the conflict—would no longer function as operational permissions in the conduct of hostilities, as these would be superseded by a determination by the commander of whether or not the strike in question constitutes a legitimate exercise of the State’s right to self-defence. The JIB framework would be reduced to regulating solely the consequences if force is used, converting it to a purely restrictive regime. The impracticalities of such an approach would be enormous, with a very real risk that commanders, who are the persons responsible for disseminating the laws of armed conflict to their forces, lose the incentive to do so.
Moreover, if, as argued by Milanović, Greenwood and Cohen, JAB applies only to strikes initiated following a period of reduced fighting or for a serious escalation, this gives rise to a new problem. It would mean that the victim State and aggressor State would shift continuously throughout an IAC. Under this approach, Ukraine could, in theory, become the aggressor, following a lull in the hostilities with Russia. This would disadvantage the victim State considerably.
As Luuk L. Snijder et al. write, because “unprovoked aggression” is often “difficult to justify on moral grounds,” States already “disguise their true objectives and falsely invoke the need for self-defense” (p. 1). However, where State leaders “sincerely perceive their actions as defensive, even when they are not[,] such defensive self-deception may [] have the functional value of enhancing leaders’ ability to persuade others and enable them to communicate with greater conviction” (p. 5). Thus, if the legal position of the States could shift from victim to aggressor throughout the IAC, it may have the effect of prolonging the conflict, and in doing so, conferring a legal and strategic advantage on the initial (true) aggressor State, contrary to the object and purpose of the JAB framework.
It also raises the question, what would be a sufficiently long pause to warrant a renewed JAB analysis? Would the Russian retreat and operational pause of three weeks following the fall of Luhansk in July 2022 suffice? Where would one draw the line?
Conclusion
In reality, few wars are fought in a linear progression of continuous hostilities. They are messy and complicated, and many involve periods of lulls, including strategic lulls which do not necessarily imply that the primary reason to engage in the conflict has vanished. In practice, decisions to resort to force are rarely determined by legal analysis alone. Insisting that the requirements of JAB must be reassessed with each individual strike, or even with some, during the course of an ongoing armed conflict risks misconceiving the role of that body of law.
The JAB framework is unlikely, in itself, to prevent the use of force where States have already chosen to engage in armed conflict. The more coherent approach, therefore, is that the constraints of JAB do not continue to govern the legality of individual strikes once an IAC has arisen. This does not imply that once the first shots are fired, the parties remain in an IAC indefinitely, and a JAB analysis will never be required for force used by those States against one another again. If the conflict truly ends, any future use of force by one of them against the other will once again be governed by JAB. However, as with the determination of the existence of an armed conflict, its continuation or termination ultimately depends on the factual circumstances.
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Olivia Flasch is an English-qualified solicitor and a Legal Consultant in Public International Law.
The views expressed are those of the author, and do not necessarily reflect the official position of the United States Military Academy, Department of the Army, or Department of Defense.
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. Authorship does not indicate affiliation with Articles of War, the Lieber Institute, or the United States Military Academy West Point.
Photo credit: U.S. Army, Staff Sgt. Brandon Rickert
