Judging Battlefield Conduct
Editors’ note: This post is based on the author’s article-length work, “The Rule of Law in Armed Conflict” published in volume 34 of the Minnesota Journal of International Law (2025).
The rule of law is an appraisal concept that purports to restrict arbitrariness in the exercise of sovereign powers. The concept is often invoked to evaluate the state of affairs within a political regime but its meaning has been debated with indecisive outcomes. Its relevance to international law is even more uncertain because no constitutional structure or processes resembling those of the national legal system exist.
This idea is not entrenched in the structure and system of international law, let alone the law of armed conflict (LOAC) that governs the conduct of hostilities. The rule of law, in situations of armed conflict, does not reside in the idea that law exists to promote the cooperative furtherance of social aims for the benefit of humanity. Instead, its role is a more restricted one that may be characterized as an emergency law designed to preserve the non-derogable elements of humanity even in the midst of warfighting.
This perspective, derived partly from the neorealistic school of thought and a pragmatic approach to international law, appears to deserve renewed attention. Geopolitical competition and technological advances are threatening to undermine the rules-based international order established in the aftermath of the Second World War. Russia’s act of aggression against Ukraine and the People’s Republic of China’s reckless behaviors in the Indo-Pacific are indicative of serious challenges posed to the existing international legal order. International law has been instrumentalized as a political language to pursue national interests or particular ideologies. Flagrant violations of fundamental norms and rules have challenged international law’s normative role as a legal system to manage international relations under the rule of law.
There is an unexpected twist, however. These challenges to the role of international law are entangled with zealous commitments to its normative architecture by legacy institutions, such as the International Criminal Court and the UN Human Rights Council. These institutions were created at the height of the liberal world order that emerged in the aftermath of the Cold War. Although post-Cold War euphoria did not last long, these institutions have continued to operate pursuant to liberal ideals espoused by the visions of international law that prevailed at their inception. Subsequent activities of these institutions in the form of judicial intervention and fact-finding have inadvertently shaped how the law of armed conflict ought to regulate the conduct of hostilities in practice.
The burgeoning practice of external reviews by international tribunals and fact-finding bodies has led to a schizophrenic development of the law of armed conflict, with a different method of application for adjudication compared to how troops are trained to operationalize it. In my recent publication, I offer a thorough analysis of how external reviewers have diverged from the normative architecture of the law due to institutional and practical constraints, while articulating the minimum standards that must be upheld when evaluating the legality of a targeting operation.
As the article is rather lengthy, this post provides key takeaways on strategic considerations in LOAC implementation for the benefit of legal practitioners and office holders who might be involved in the adjudication of battlefield conduct.
From a Military Code to International Codification
Strategic considerations have always been integral to normative developments in the modern law of armed conflict. The first codification of the laws of war by Francis Lieber, issued as General Orders No. 100 to the Union Army during the 1861-1865 U.S. Civil War, assumed, at least in part, a form of strategic warfare as a means of achieving military effects and objectives on contested issues. The adoption of the St Petersburg Declaration in 1868, which paved the way for the regulation of weapons by means of international agreement, was an outcome of mixed strategic and humanitarian considerations surrounding the rapid technological advancement in weaponry (p. 449-55). Similar strategic calculations led to the convening of the 1899 and 1907 Hague Peace Conferences, extending the regulatory reach to expanding bullets, asphyxiating or deleterious gases, and for a short period of time, the use of balloons for aerial bombardment.
Built on such strategic considerations, LOAC emerged essentially as a self-regulatory regime that relied on military acquiescence in a practical and workable limit on the violence of warfare and the internal disciplinary structures embedded within the military profession for implementation. As David Kennedy has observed, the rules thus developed have come to be seen “less as an external or ex post judge of military behavior than as a vocabulary for arguing about the legitimacy and illegitimacy of military conduct” (p. 86).
Early efforts to codify specific rules governing aerial bombardment, which came subsequently to be known as targeting operations, did not come to fruition due to divergent and evolving practices in military operations and technological limitations in controlling lethal effects. The comparatively fine-grained rules, as reflected in Part IV of Additional Protocol I to the Geneva Conventions, became practicable only when technology matured to enable military forces to direct projectiles and explosives with a degree of accuracy.
The codification of targeting law and its crystallization under customary international law has had a two-fold impact. First, it has helped standardize how military forces are to protect civilians while conducting targeting operations and facilitate its implementation with a degree of uniformity. The underlying logic of the law, in this sense, is fairly simple. One must not plan, authorize, or conduct attacks when, based on a good faith assessment of the information available at the time, civilians are known to be targeted, civilian casualties are reasonably estimated to be excessive to the anticipated military advantage, or there are other means reasonably available to avoid or minimize civilian casualties. The codified rules address humanitarian concerns about the violence of warfare but one must not forget that these rules are, at the same time, designed to uphold the imperative of military efficiency and strategic wisdom that humankind has come to appreciate through the history of wars.
Second, the integration of a military code into the discourse of international law has opened an avenue for the review and evaluation of battlefield conduct by external entities, such as judicial institutions, fact-finding bodies, third-party States, and humanitarian organizations. This implication was not entirely unexpected. Geoffrey Best, for example, suspected that codification efforts might turn into “a handy aid to vilification” rather than a meaningful restraint on the conduct of hostilities (p. 47). Nevertheless, most codification efforts precede the birth and growth of international monitoring institutions, such as the International Criminal Court and the UN Human Rights Council. What may have been unexpected, therefore, is how these institutions may independently develop ingenious methods to interpret and apply the lawyerly crafted rules of targeting law to contemporary warfare.
The “Rendulic” Rule
The law of armed conflict is not entirely devoid of guidance on the methods of adjudication that external reviewers must apply in evaluating the legality of battlefield conduct. Drawing from the trial of General Lothar Rundulic at the Nuremberg proceedings, LOAC has established that the legality of military decisions made on the battlefield is not to be evaluated with the wisdom of hindsight based on the objective facts that came to light afterward. The Tribunal acquitted General Rundulic of charges relating to the “scorched earth” campaign he carried out in the Norwegian province of Finmark under the impression that the Russian troops were in pursuit. Although it turned out that Russian forces did not follow up the retreat to the extent anticipated, the Tribunal considered that fact had little impact on its ruling as long as the defendant had “acted within the limits of honest judgment on the basis of the conditions prevailing at the time” (p. 1297).
This judicial doctrine, which came to be called as the Rundulic Rule, has extended beyond the narrow set of circumstances faced by General Rundulic and, as detailed by Sean Watts in his commentary, has subsequently been integrated as a primary rule of conduct in various law of war treaties (p. 170-72). It is a pivotal standard to which external reviewers must adhere when evaluating military decision-making under the modern law of armed conflict. It also operates as an inherent limit on humanitarian efforts to regulate the conduct of warfare through an external review process due to the following three reasons.
First, the idea of objectively assessing the reasonableness of military decision-making finds little support in an environment where decision-makers do not enjoy a high degree of control over the circumstances confronting them. Although regrettable, civilian casualties inevitably arise due to targeting errors and the adversary’s failure to keep civilians and military objectives further apart. The failure to verify military targets or minimize civilian harm does not necessarily make targeting decisions unreasonable as long as precautions are taken to the extent feasible under the attendant circumstances. While military decision-makers must act with due diligence and in good faith for reasons of military necessity, battlefield uncertainties render the application of reasonableness standards ill-suited to the review of targeting decisions.
Second, intelligence-driven targeting practices in modern military operations impose practical impediments to the gathering of information necessary for adjudication. Military intelligence sharing is generally prohibited without authorization and States are not obliged to comply with requests for such information unless they are so compelled by the UN Security Council acting under Chapter VII authority (as was the case with the international criminal tribunals established for the former Yugoslavia and Rwanda).
In practice, the lack of cooperation leads external reviewers to rely heavily on circumstantial evidence. But forensic evidence from the battlefield tends to be difficult to gather due to damage and destruction or the actions of the adversary. Concluding an attack was indiscriminate based on a lack of indications or evidence that would have characterized the target as a military objective turns the logic of the law on its head. The Hague civil court took this approach in its judgment on the battle of Chora and the UN Human Rights Council’s commissions of inquiry also frequently do so (see references cited at n. 84-87).
Third, external reviewers are not necessarily trained in military tactics, maneuvers, threat assessment, and logistical sustainment. They are not well equipped to assess the military values of the target, an acceptable level of risk to civilians, or practical steps that could have been taken to verify the military objective and to avoid or minimize civilian harm. Without such practical insights, adjudication risks error in the application of the law by failing to make a contextual evaluation of military objectives, information and resources available at the time, and the entirety of battlefield conditions. Such a contextual evaluation of each attack becomes practically untenable when hundreds of sorties are coordinated, managed, and launched every day of fighting in large-scale combat operations.
Judicial Deference
All these practical and institutional constraints cast doubt on the ability of external reviews to adjudicate the legality of targeting operations. Adjudication is doomed to fail, or worse, to become instrumentalized as a means of vilification by simply regurgitating applicable rules without having regard to operational context. Informed by the Rendulic Rule, external reviews of targeting decisions must be confined to cases where systematic violations can be objectively established without intruding into the commander’s lawful decision-making space. An objective, consistent, and non-arbitrary application of the law, as demanded by the ideals of the rule of law, requires external reviewers to be deferential to the professional judgement made by military commanders based on operationally relevant information available at the time when authorizing or directing attacks.
Judicial deference is especially warranted where external reviewers lack expertise in military operations or access to sufficient information necessary to make objective findings (p. 91-97). This means that belligerent parties enjoy broader discretion for the deprivation of life and liberty than in peacetime. To establish a violation of their legal obligations, clear and convincing evidence must be presented to meet a high standard of proof, as was so demanded when the Eritrea-Ethiopia Claims Commission determined responsibility for war reparations (paras. 45-46) and the prosecution considered cases for trial at the Yugoslav Tribunal (para. 5).
With this deferential approach, external reviewers must construe each rule carefully to enable them to draw conclusions from objectively verifiable facts. Rather than adopt a one-size-fits-all approach, external review needs a more systematic method of inquiry, for example, by seeking to identify patterns of misconduct and repeated errors in the targeting process resulting from the failure to rectify them. These patterns may be insufficient to establish a deliberate targeting of civilians but the failure to rectify these problems can be probative of the failure to exercise feasible precautions to verify military targets and avoid or minimize civilian harm.
The commander’s intent to accept the risk of harm to civilians within the bounds of the law must not be misconstrued as reckless disregard for the danger posed to civilians. One may argue that criminal accountability under customary international law has expanded to encompass reckless targeting of civilians and civilian objects (p. 665), drawing uncritically on the Yugoslav Tribunal’s ruling in Prosecutor v. Galić (paras. 54, 596) and the International Committee of the Red Cross’s commentary (para. 3474).
However, as Brian Cox and Jens Ohlin previously discussed, there are obvious flaws in such an expanded reading. Adopting the recklessness standard would turn the act of launching a military operation knowing and accepting the risk of harm to civilians into a criminal offense when it would otherwise be considered lawful. To avoid this pitfall, adjudication must instead focus on establishing that the target could not have been a military objective or civilian casualties could not have been justifiable, based on verifiable evidence. In other words, the commander’s willful intent must be found in the absence of intent to target military objectives.
Further, when assessing circumstantial evidence, care must be taken of contextual variables, including factors beyond the commander’s control that might account for civilian casualties. Without access to targeting information, external reviewers have no choice but to seek situationally relevant information such as the forensic analysis of ballistic trauma, the physical condition of the victims, and their distance from areas of active hostilities. However, as Geoff Corn has observed, civilian casualties may result unintentionally, contrary to the purpose or knowledge of the attacking force at the time they acted (p. 159-60). To circumvent this evidentiary challenge, external reviewers must turn their attention to the lack of indications of possible military use or value, as the Eritrea-Ethiopia Claims Commission did in evaluating the legality of attacking electric power stations (paras. 117-19).
Concluding Thoughts
The limited ability to judge battlefield conduct due to practical and institutional constraints means that adjudication must circle along the outer layers of forbidden characteristics rather than intruding into grey areas where the commander’s decision is reasonably contestable. One may bemoan the risk of impunity and the accountability gap that may result from judicial deference. However, we must not forget that LOAC is essentially a self-regulatory body of law with its roots in military codes to guide the conduct of hostilities. Its effectiveness hinges heavily on the discipline of belligerent parties themselves and their readiness to implement it in good faith. A gap, if there is any, simply represents an inherent limit of international law as a normative instrument to regulate the conduct of hostilities.
Any attempt to cross this line to advance humanitarian agendas by, for example, lowering evidentiary standards and shifting the burden of proof, risks undermining confidence in the law among States. There are early indications of this problem such that the President of the International Committee of the Red Cross felt compelled to urge States to reinvigorate political commitment to the law. Appealing to their respect for the law will prove hollow unless the underlying causes are addressed. It is time to realize that the project of a liberal world order has lost touch with the reality of international relations. The regulation of battlefield conduct through international law should align with the pace that States consider adequate to protect their national interests.
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Hitoshi Nasu is a Professor of Law in the Department of Law at the United States Military Academy.
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.
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Photo credit: U.S. Army, Spc. Brandon Vasquez
