Belligerent Reprisals Series – Changing the Paradigm to Rein in Retaliation in Armed Conflict
Editors’ note: This post introduces a series related to Francesco Romani’s book Belligerent Reprisals from Enforcement to Reciprocity published by Cambridge University Press.
In its centuries-old development, modern international humanitarian law (IHL) has progressively distanced itself from the idea of reciprocity. This trend has culminated in recent years, when the claim that the behaviour of one party to an armed conflict may have a bearing on the IHL obligations of another party has lost legal traction as well as moral standing.
International tribunals such as the International Court of Justice and the International Criminal Tribunal for the former Yugoslavia have stressed the “absolute” and “fundamental” nature of many (if not most) IHL rules, which create obligations said to be “unconditional” and “essentially of an erga omnes character.” Similarly, the International Committee of the Red Cross (ICRC) Customary IHL Study states that “[t]he obligation to respect and ensure respect for international humanitarian law does not depend on reciprocity.” Authors such as Professors Sean Watts and Bryan Peeler have recently investigated the continuing role of reciprocity in structuring IHL. But in general, there is strong resistance to the idea that compliance with IHL rules by one belligerent ultimately depends on a counterpart’s respect for its own obligations (UNSC Res. 2730 (2024), para. 2; ICRC 2024 Challenges Report, p. 1363).
Despite this solid consensus, parties to armed conflict increasingly seem to justify their alleged failure to abide by IHL (or their threat not to do so) on the grounds that their enemy is breaking the laws of war. The phenomenon is not limited to one type of armed conflict or actor. States and non-State actors alike are increasingly stressing that their war-time conduct (and therefore their compliance or not with IHL rules) will mirror that of their adversary.
Examples, drawn from different contexts, are particularly telling. In the context of the international armed conflict between the Russian Federation and Ukraine, references to so-called “symmetrical responses” to enemy’s attacks characterized the statements released by both belligerents in the spring of 2025 (here, here, and here). And during the non-international armed conflict between Israel and Hezbollah, the Lebanese armed group warned it would launch missiles on Israeli towns and settlements that had not been previously targeted if Israeli strikes continued to kill Lebanese civilians.
Belligerent Reprisals: Back on Stage?
These occurrences have brought back into international legal discourse the notion of belligerent reprisals including its definition, its regulation, and the conditions (if any) for its continued permissibility under modern IHL. In essence, a belligerent reprisal is as “an act that would violate the laws of armed conflict, were it not for its being taken in response to a previous unlawful breach of that body of rules by the counterpart” (Romani, p. 4). Said otherwise, belligerent reprisals represent retaliatory breaches of the laws of war that are justified to the extent they follow a previous wrongdoing, pursue a certain objective, and respect certain conditions. The underlying assumption is that, in the absence of effective mechanisms to ensure compliance with the laws of war, the party wronged by an IHL violation has some entitlement to take the matter in its own hands and react to enemy breaches by disobeying the law in turn.
Over the years, international treaties, case law, and scholarship have considerably curtailed the possibility for a party to an armed conflict to resort to belligerent reprisals. As Professor Michael Schmitt has explained in a recent post on Articles of War, limitations to that effect relate both to the permissible targets of belligerent reprisals, and to the substantive and procedural requirements that these measures must follow. These strict parameters are intended to constrain and ultimately reduce recourse to belligerent reprisals by parties to armed conflict.
However, the fact that belligerents’ language and behaviour are constantly modelled on the counterpart’s actions signals a much more pervasive tendency to read reciprocal considerations into the operationalization of IHL. Can this tendency to resort to self-help measures be explained solely on the basis of factors such as the absence of enforcement mechanisms, the supposed death of IHL (see, e.g., here and here), or the lack of faith in a crumbling international legal order? The answer, in my view, lies elsewhere, and has to do with the way in which international law thinks of belligerent reprisals. In this sense, we are confronted with a failure of formalizing, rather than of applying, IHL.
Formalizing the Purpose of Belligerent Reprisals
Although important questions still linger on the substantive and procedural aspects of belligerent reprisals (ICRC, Customary IHL Study, rules 145-48 and related commentaries), one requirement for the adoption of such measures remains virtually unchallenged. I am referring to the requirement that belligerent reprisals must have an enforcement function. That is, a party must take them “only for the purpose of inducing the adversary to comply with the law” (ICRC, Customary IHL Study, commentary to rule 145).
This position has taken decades of intellectual refinement to crystallize. In the past, authors such as Professors Julius Stone and (at least in a phase of his thought) Hersch Lauterpacht maintained that belligerent reprisals could have a law-making function. Looking at the practice in the two World Wars, they argued that retaliatory violations of the laws of war could work as a way to bring about change in IHL norms that were outdated but that States could not modify through multilateral processes.
And yet, legal commentators have largely abandoned this minority view. Instead, a consensus has settled whereby belligerent reprisals are only legitimate if they work as coercive measures to induce the wrongdoing enemy to resume compliance with IHL. Far from structuring only the purpose of belligerent reprisals, this enforcement-based understanding has also shaped the regulation of such measures. It is no coincidence that various requirements of belligerent reprisals (such as proportionality, subsidiarity, and termination) reflect closely those that apply to countermeasures (the paradigmatic enforcement tool of self-help under international law, as codified by the International Law Commission in Articles 49-53 of the Articles on the Responsibility of States for Internationally Wrongful Acts).
Challenging the Enforcement-based Understanding of Belligerent Reprisals
It is clear that formalizing belligerent reprisals in light of the enforcement purpose and based on the blueprint of countermeasures aligns with an IHL framework seen as unconditional and intransgressible. Arguing that retaliatory breaches can only serve the purpose of inducing compliance with (and therefore re-affirming the cogency of) IHL norms has the advantage of immunizing the legal framework from the risk of repeated violations (including justified ones). And yet, I am convinced that this interpretation does not adequately reflect the purposes and function that parties to armed conflict attach, as a matter of law, to belligerent reprisals.
A careful analysis of the statements and behaviours of parties to armed conflicts (both international and non-international) suggests these actors attach a panoply of different meanings to belligerent reprisals. These include: punishing the enemy belligerent for having violated the law; bringing about the cessation of an unlawful conduct; re-establishing the equality of arms between belligerents that the original violation of IHL has altered; and even clarifying the rules by which belligerents fight. These meanings develop over time. As belligerents get to “know” each other during the military confrontation, they refine their ability to communicate “by deed” (Schelling), and learn how to interpret the counterpart’s retaliatory behaviours and “unfriendly unilateralism” (Hakimi).
Such purposes have little do with peacetime countermeasures and the enforcement function underlying them. Rather, these purposes are closely associated with the objectives traditionally implemented by measures inspired by reciprocity (both in its negative and in its positive form), and especially the aim of establishing and maintaining the equality of rights and obligations between parties to armed conflict. To be clear, this would not lead to an outcome where key IHL provisions are suspended or terminated. Rather, looking at belligerent reprisals through the reciprocity lens allows us to understand which juridical values are protected by the adoption of such measures, and therefore to assess the role (if any) they have in the international legal order.
Belligerent Reprisals as Tools to Negotiate and Agree on Standards of Conduct
In this sense, the purposes associated with belligerent reprisals extend well beyond the limited idea of enforcing existing IHL norms. Scholars have long been aware of the limitations embedded in the idea that reprisals have an enforcement function. To bypass this problem, authors such as Professors Kalshoven and Greenwood have suggested that belligerents can adopt reprisals with different concrete purposes in mind, as long as their primary concern is that of inducing compliance with the breached norm.
This suggestion has several problems. First, it presupposes that the law to be enforced is always clear and well settled, whereas divergences may exist between parties to an armed conflict on the applicability and interpretation of a norm, or on the contours of its implementation in any given case. Second, it does not clarify which IHL provisions should be upheld by the adoption of belligerent reprisals. Should it be the full range of existing IHL obligations? Although ideal and (at least to some extent) facilitated by the development of customary norms, this solution would arguably be at odds with the consent-based premises in the application of international treaties and norms (including in the field of armed conflict). Would reprisals then aim at re-affirming only those rules by which both belligerents are bound? But this would result in a paradoxical outcome, insofar as an instrument designed to uphold IHL may, in practice, reduce the protections afforded by that legal regime.
If one looks at the arguments and justifications of parties to armed conflicts, the re-affirmation of the legal order appears (when at all present) more as a by-product than as the key concern of the adoption of belligerent reprisals. By retaliating against enemy conduct, a belligerent may signal its opposition to a certain interpretation of an IHL norm or react to new dynamics in the conduct of hostilities (such as by directing attacks against targets previously unaffected by hostilities). By modulating its response, a belligerent may also hint at paths to immunize certain targets from attack or reduce the overall level of hostilities.
In all these cases, focusing solely on the purpose of cessation of IHL breaches fails to capture the subtlety of the meanings associated with retaliatory conduct. Attributing to belligerent reprisals only an enforcement function overlooks the fact that parties to a conflict may disagree on the scope and meaning of a given IHL rule. In such situations, and somewhat paradoxically, retaliatory breaches in the form of reprisals would be the only way for belligerents to craft and agree on a common understanding of the standards of conduct to be followed in the military confrontation.
Implications of Re-Conceiving the Purposes of Belligerent Reprisals
Arguably, embracing the reciprocity-inspired understanding of belligerent reprisals would help answer several questions that still haunt the regulation of these measures. In this series, I have invited two experts to investigate some of the pressing aspects that would be impacted the most by a new formalization of the purpose of belligerent reprisals. Stuart Casey-Maslen will tackle the topic of reprisals from the angle of weapons law, addressing different situations where the unlawful use of a lawful weapon, or even the use of an unlawful weapon, may be justified. Veronika Bílková will delve into the thorny issue of belligerent reprisals in non-international armed conflict, shedding light on the additional problems that the measure creates when non-State armed groups enter the picture. Finally, a concluding post by myself will consider the policy implications of this new formalization of belligerent reprisals, explaining how a reciprocity-inspired understanding of these measures may suggest new and sounder initiatives to govern, constrain, and perhaps ultimately dispense with retaliation in warfare.
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Dr Francesco Romani is a Research Fellow at the Geneva Academy of International Humanitarian Law and Human Rights. He is the author of Belligerent Reprisals from Enforcement to Reciprocity: A New Theory of Retaliation in Conflict (CUP, 2024).
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: Marine Corps Lance Cpl. Rodney Frye
