Martens Clause: Meaning and Legal Effect in Armed Conflict

Introduction

The Martens Clause is a principle of international humanitarian law that preserves legal protection for civilians and combatants when particular situations are not expressly regulated by treaties governing armed conflict. First incorporated into the preamble of the 1899 Hague Convention (II), it affirms that international legal principles continue to apply through established custom, the principles of humanity, and the dictates of public conscience.

The clause is recognized as part of customary international law, although its precise normative consequences remain disputed. It prevents the silence of a particular treaty from being treated as the disappearance of legal restraints on warfare. However, it does not automatically prohibit every weapon, military practice, or method of warfare that lacks a specific treaty prohibition.

Its legal significance concerns the relationship between codified rules and the broader principles governing military conduct. International humanitarian law contains detailed provisions protecting persons and restricting the conduct of hostilities, but no treaty can anticipate every circumstance arising during armed conflict. The Martens Clause addresses the continuing protection afforded by international law where treaty provisions are incomplete.

The central controversy concerns whether the clause principally preserves existing customary obligations, guides the interpretation of humanitarian rules, or gives independent normative force to the principles of humanity and public conscience.

International jurisprudence, particularly the International Court of Justice's 1996 Nuclear Weapons Advisory Opinion, provides important guidance while leaving the precise extent of its independent legal effect unsettled.

1. Meaning and Legal Effect of the Martens Clause

The Martens Clause originated as a declaration that persons affected by armed conflict remain protected by international legal principles even when specific circumstances fall outside the regulations adopted by states. Its original formulation refers to the usages established between civilized nations, the laws of humanity, and the requirements of public conscience. Although its terminology reflects nineteenth-century international law, the provision expresses a continuing concern: treaty codification cannot be regarded as an exhaustive statement of every applicable legal obligation.

The clause is significant because international humanitarian treaties regulate different subjects with varying degrees of specificity. Some provisions establish precise prohibitions, while others express broader obligations requiring interpretation in particular circumstances. Where a treaty does not address a particular military practice, applicable customary rules and other relevant international legal obligations must still be considered.

The expression "principles of humanity" refers to humanitarian considerations reflected throughout the law of armed conflict, including the protection of persons who are not participating in hostilities and restrictions on unnecessary suffering. The "dictates of public conscience" introduce a more contested concept concerning collective humanitarian judgments and their possible influence on international legal obligations. Their recognition in the clause does not establish that they independently create binding prohibitions in every circumstance.

The distinction is particularly important when assessing the legality of military conduct. International law does not generally require every military action to be expressly authorized by a dedicated treaty provision. Equally, the absence of a weapon-specific prohibition does not establish legality where other applicable international rules restrict or prohibit the weapon's employment.

The Martens Clause must consequently be understood within the broader system of international humanitarian law, which regulates armed conflict through treaty obligations and customary rules. Its minimum legal significance lies in preserving the relevance of those obligations beyond the express provisions of a particular treaty. Whether humanity and public conscience add further substantive restrictions remains a separate question.

The International Committee of the Red Cross (ICRC) recognizes this distinction in its 2025 Commentary on Article 158 of the Fourth Geneva Convention. The Commentary identifies the clause's customary status while acknowledging competing interpretations of its legal consequences. It also explains that the provision prevents an inference that conduct omitted from a treaty must necessarily be permitted (ICRC, 2025, paras. 7035–7044).

2. Origins and Treaty Development of the Martens Clause

The Martens Clause emerged during the codification of the laws and customs of land warfare in the late nineteenth century. European states had previously attempted to establish common rules through the Brussels Conference of 1874, which produced a declaration addressing combatant status, military occupation, prisoners of war, and the conduct of hostilities. The declaration was not adopted as a binding convention, partly because participating states disagreed over the rights of occupying powers and the legal position of populations resisting invasion.

Those disagreements reappeared at the First Hague Peace Conference in 1899. The principal controversy concerned whether the proposed regulations adequately protected inhabitants of occupied territory and how international law should classify persons resisting an invading or occupying army without satisfying the prescribed conditions for lawful belligerents.

Fyodor Fyodorovich Martens, a Russian diplomat and international lawyer who chaired the relevant subcommission, proposed a declaration intended to overcome the disagreement. The resulting compromise allowed the conference to adopt rules on land warfare without determining every contested question concerning resistance and occupation.

2.1. The 1899 Hague Compromise

Belgium and other smaller powers feared that the proposed rules would favor states possessing substantial military forces. Their concerns were particularly acute because smaller countries faced the possibility of rapid occupation by more powerful neighbors. A restrictive definition of lawful belligerents could deny important protections to inhabitants resisting occupation outside established military organizations.

The negotiations addressed the position of regular armed forces, militias, volunteer corps, and inhabitants spontaneously taking up arms against an invading enemy. The proposed regulations recognized certain categories of belligerents while leaving other forms of resistance insufficiently resolved. Major military powers opposed broader recognition that might undermine the security of occupying armies or permit attacks by persons operating outside conventional military structures.

Belgium's Auguste Beernaert challenged the proposed arrangements, particularly their implications for occupied populations. The disagreement involved the extent of an occupying power's authority and the classification of inhabitants who resisted military occupation. The opposing delegations were unable to reach agreement on a substantive formulation resolving every disputed situation.

Martens' proposal offered a compromise. In cases not covered by the adopted regulations, inhabitants and belligerents would remain under the protection of the principles of international law. The declaration was connected to the interpretation of Articles 1 and 2 of the Hague Regulations, concerning the categories of lawful belligerents and the spontaneous resistance of inhabitants of territory not yet occupied.

The compromise did not itself establish an unrestricted right of armed resistance in occupied territory. Nor did it determine that every person resisting occupation would enjoy lawful combatant or prisoner-of-war status. Those questions remained subject to the applicable rules governing participation in hostilities and the treatment of persons captured during conflict.

Antonio Cassese's historical analysis emphasizes the diplomatic character of the arrangement. The declaration enabled states with opposing positions to accept the convention while leaving important questions unresolved. Its subsequent prominence in humanitarian law cannot be explained solely by the intentions of the delegates who negotiated it (Cassese, 2000, pp. 193–198).

The circumstances of its adoption reveal a significant feature of the development of the law of armed conflict. International agreements may preserve disagreement through carefully formulated principles while allowing more specific rules to be adopted. The legal significance of such formulations may subsequently develop through state practice, treaty negotiations, and judicial interpretation.

2.2. Reaffirmation in the Hague and Geneva Instruments

The preamble to the 1907 Hague Convention (IV) reproduced the central formulation of the Martens Clause. Its inclusion reaffirmed that the codified regulations governing land warfare did not exhaust the applicable principles of international law. Later humanitarian instruments incorporated related formulations, sometimes with changes reflecting their particular purposes and legal scope.

The four Geneva Conventions of 1949 contain corresponding language in their provisions governing denunciation. Article 63 of the First Convention, Article 62 of the Second, Article 142 of the Third, and Article 158 of the Fourth preserve the relevance of principles of the law of nations notwithstanding a state's denunciation of the relevant convention.

These provisions distinguish obligations arising from a particular treaty from legal protections that continue independently under international law. Their inclusion does not mean that every treaty obligation necessarily survives denunciation unchanged. Rather, they recognize that withdrawal from a convention does not extinguish obligations established through other applicable sources.

A more direct formulation appears in Article 1(2) of Additional Protocol I of 1977. It provides that civilians and combatants remain under the protection and authority of the principles of international law derived from established custom, the principles of humanity, and the dictates of public conscience in cases not covered by the Protocol or other international agreements.

The placement of the clause in an operative article distinguishes Additional Protocol I from the earlier Hague formulation. It forms part of the treaty obligations accepted by the Protocol's parties, while the customary status of the clause provides a separate basis for its recognition beyond that treaty relationship.

Additional Protocol II, concerning certain non-international armed conflicts, includes a related declaration in its preamble. It affirms that the human person remains under the protection of the principles of humanity and the dictates of public conscience in cases not covered by the law in force. Unlike Article 1(2) of Additional Protocol I, this formulation does not expressly refer to established custom.

The different wording and treaty scope are legally significant. Additional Protocol II does not establish every obligation applicable in non-international armed conflicts, nor does its preambular reference independently extend all provisions of Additional Protocol I to those conflicts. Common Article 3 of the Geneva Conventions and applicable customary international humanitarian law provide additional protection according to their own scope and legal requirements.

The 1980 Convention on Certain Conventional Weapons also incorporates the Martens Clause in its preamble. Its inclusion in an instrument addressing weapons considered excessively injurious or indiscriminate connects the clause with the legal regulation of means and methods of warfare.

The successive treaty formulations demonstrate the clause's continuing recognition beyond its original connection to occupation and combatant status. They also show that humanitarian protection remains relevant where legal instruments do not comprehensively regulate particular circumstances. The legal effect of the clause must nevertheless be established through the applicable treaty framework and customary international law, rather than presumed from its repeated appearance alone (ICRC, 2025, paras. 7032–7036).

3. The Martens Clause as Customary International Law

The Martens Clause is recognized as having acquired the status of customary international law. This recognition is significant because customary obligations may apply independently of participation in a particular treaty. Its repeated incorporation into humanitarian instruments and treatment by international courts support the conclusion that its protective function is not confined to the states originally party to the 1899 Hague Convention.

Customary international law is generally identified through a general practice accepted as law. The International Law Commission's 2018 Conclusions on Identification of Customary International Law distinguish two constituent elements: state practice and acceptance of that practice as legally required or permitted, commonly termed opinio juris (ILC, 2018, Conclusion 2).

The distinction between customary recognition of the clause and the existence of particular substantive prohibitions is fundamental. Even where the clause itself forms part of customary international law, it does not follow that every humanitarian proposition associated with its wording constitutes a separate customary obligation.

The International Court of Justice addressed the clause's customary character in its 1996 Nuclear Weapons Advisory Opinion. In paragraph 84, the Court identified the Martens Clause, reaffirmed in Article 1 of Additional Protocol I, as an example of a provision reflecting pre-existing customary law. The Court did not use that recognition to establish that humanity and public conscience automatically create specific prohibitions independently of other legal requirements.

Customary international humanitarian law also operates across different categories of armed conflict, although the scope of individual rules must be established separately. Additional Protocol I principally concerns international armed conflicts, whereas Additional Protocol II applies to a defined category of non-international armed conflicts.

Common Article 3 and applicable customary rules provide protection in non-international conflicts beyond the narrower treaty conditions governing Additional Protocol II.

The relevance of the Martens Clause to both categories does not erase those distinctions. Particular obligations concerning combatant status, detention, targeting, and methods of warfare must still be assessed according to the applicable legal framework. A rule established for international armed conflict cannot automatically be extended to every non-international conflict merely by invoking humanity or public conscience.

The relationship between the clause and the formation of customary international law becomes especially important when a proposed humanitarian restriction enjoys substantial normative support but limited evidence of corresponding state practice.

Some scholars have argued that humanitarian considerations may influence the relative significance attributed to practice and opinio juris in determining whether a customary rule has emerged. That proposition remains contested. Recognition of the Martens Clause does not establish a general exemption from the ordinary requirements for identifying customary international law.

The ICRC's 2025 Commentary reflects this distinction. It identifies the clause's customary status while treating the proposition that it accelerates customary-law formation as one among several interpretations rather than an established exception to the law of sources (ICRC, 2025, paras. 7035–7039).

4. Competing Interpretations of Its Normative Force

The principal controversy surrounding the Martens Clause concerns the legal consequences of its references to humanity and public conscience. International courts and scholars recognize its continuing relevance, but they disagree over whether it merely preserves existing legal obligations, influences interpretation, or supports the recognition of additional international legal standards.

These approaches are not necessarily mutually exclusive. A legal interpreter may accept that the clause preserves customary obligations while also recognizing its relevance to the interpretation of existing humanitarian rules. The sharper disagreement arises when humanitarian considerations are invoked as an independent basis for prohibiting conduct without establishing another recognized legal source.

The distinction has practical consequences. A restrictive interpretation directs the decision-maker toward existing treaty and customary obligations. An interpretative approach may affect how those obligations apply to uncertain circumstances. An expansive interpretation could support a prohibition based more directly on the principles of humanity or the dictates of public conscience.

The clause's wording accommodates these competing readings, but their legal authority is not identical. Their persuasiveness depends on treaty language, state practice, judicial reasoning, and the broader principles governing the identification and interpretation of international law.

4.1. Treaty Silence and the Preservation of Customary Law

The restrictive interpretation understands the Martens Clause principally as a safeguard against treating humanitarian treaties as exhaustive. Under this approach, the absence of a particular prohibition in a treaty does not remove restrictions established by customary international law or another applicable legal obligation.

This interpretation responds to an argument a contrario: because a treaty regulates certain conduct, practices not mentioned in that treaty must necessarily be lawful. The clause prevents that inference by preserving the continuing relevance of international law outside the express terms of the instrument concerned.

The distinction does not establish the opposite proposition that all military conduct requires express authorization. A state's legal obligations must still be identified through the applicable sources of international law. The absence of a prohibition in one treaty may be relevant to that inquiry, but it does not determine whether other legal restrictions apply.

Antonio Cassese criticized the restrictive interpretation for giving the clause limited independent significance. Customary international law ordinarily continues to operate alongside treaty law without requiring an express treaty provision preserving its existence. A construction confined to that proposition risks making the clause largely declaratory (Cassese, 2000, pp. 192–193).

Its practical significance should nevertheless not be dismissed. The provision expressly rejects the idea that adopting detailed rules of warfare exhausts the relevant legal restraints. That function may be valuable when a particular treaty addresses only certain weapons, military practices, or categories of protected persons.

The restrictive approach remains compatible with the ICRC's 2025 Commentary, which identifies the continuing validity of customary law alongside treaty law as the minimum significance of the clause (ICRC, 2025, paras. 7042–7043).

4.2. Humanity and Public Conscience in Legal Interpretation

A second approach recognizes the Martens Clause as relevant to the interpretation of existing international humanitarian law. Where a provision is ambiguous or a general rule must be applied to unfamiliar circumstances, the principles of humanity and public conscience may assist in determining its meaning.

This interpretation gives the clause a more active legal function without treating humanitarian considerations as unrestricted sources of new obligations. It operates within the established international legal system, where treaty provisions and customary rules must be interpreted and applied according to their content, scope, and purpose.

The relationship between humanitarian protection and military necessity illustrates the issue. International humanitarian law does not prohibit every form of suffering associated with armed conflict, but it restricts the means and methods through which military objectives may be pursued. The protection of civilians and the prohibition of unnecessary suffering impose established legal limitations on military conduct.

Humanitarian considerations may influence the application of these restrictions to circumstances not anticipated when particular instruments were adopted. They do not, however, permit a decision-maker to disregard the wording of a treaty or transform a general humanitarian aspiration into a binding prohibition without adequate legal justification.

The dictates of public conscience present additional interpretative difficulties. International resolutions, diplomatic declarations, treaty negotiations, and institutional positions may provide evidence of prevailing humanitarian judgments. Their significance depends on whether they reflect legal conviction, political preference, moral opposition, or proposals for future legal regulation.

A resolution condemning a weapon, for example, may express substantial humanitarian concern without independently establishing a customary prohibition. Its relevance to legal interpretation depends on its language, the circumstances of its adoption, the positions of participating states, and its relationship to other evidence of international law.

The interpretative approach consequently preserves an important distinction between the moral considerations influencing humanitarian law and the legal methods through which particular obligations are identified. The ICRC recognizes this approach as one of the principal interpretations of the Martens Clause (ICRC, 2025, para. 7040).

4.3. Independent Normative Force and Customary-Law Formation

More expansive interpretations attribute independent legal significance to humanity and public conscience. Under these approaches, the Martens Clause may be understood as recognizing standards capable of restricting military conduct beyond prohibitions already established through treaty law or the ordinary customary-law process.

The strongest versions suggest that the clause recognizes humanity and public conscience as distinct sources of international obligations. A related interpretation regards these considerations as capable of influencing the identification or development of customary rules without treating them as wholly separate sources of law.

Antonio Cassese rejected the view that the clause created two additional sources of international law. He nevertheless proposed that humanitarian considerations could influence the development of customary law by increasing the significance of opinio juris relative to the evidence of established practice (Cassese, 2000).

The proposal addresses a difficulty arising in the regulation of warfare. States may recognize serious humanitarian dangers before a substantial body of practice develops concerning a new weapon or military method. Insisting on extensive historical practice in every circumstance may delay the recognition of protective rules despite strong evidence that states regard particular conduct as unlawful.

Yet the existence of opinio juris cannot be established merely by demonstrating moral opposition. Statements condemning military conduct may reflect political objectives, humanitarian preferences, or proposed legal changes rather than acceptance of an existing obligation.

Theodor Meron's examination of the clause similarly demonstrates the range of interpretations concerning humanity, public conscience, and customary-law development. His analysis reflects the difficulty of determining the clause's independent legal effect within the conventional structure of international legal sources (Meron, 2000).

An expansive interpretation must also confront the problem of identifying public conscience. International society contains differing legal traditions, political priorities, and moral judgments. Broad agreement that a practice is undesirable does not necessarily establish consensus on the precise legal restrictions governing it.

The legal question is not whether humanitarian concerns are relevant. Their significance in international humanitarian law is well established. The unresolved issue is whether the Martens Clause permits those considerations to generate binding obligations through a process distinct from the recognized methods of international lawmaking.

The ICRC's 2025 Commentary acknowledges the competing theories without treating the broadest interpretation as settled law. Its discussion preserves the distinction between the clause's recognized legal status and the disputed proposition that it independently creates substantive prohibitions (ICRC, 2025, paras. 7037–7044).

5. The ICJ's 1996 Nuclear Weapons Advisory Opinion

The International Court of Justice gave its most influential treatment of the Martens Clause in the Advisory Opinion on the Legality of the Threat or Use of Nuclear Weapons, delivered on July 8, 1996. The United Nations General Assembly had asked whether the threat or use of nuclear weapons was permitted under international law in any circumstance.

The Court examined the United Nations Charter rules governing the threat or use of force, relevant treaty obligations, customary international law, and the rules applicable during armed conflict. Its inquiry distinguished the legality of resorting to force, governed by jus ad bellum, from the legality of the means and methods employed during hostilities, governed by jus in bello.

The distinction was essential because a lawful claim of self-defense does not remove the obligation to comply with international humanitarian law. Conversely, compliance with the rules governing the conduct of hostilities does not independently establish that resorting to force was lawful under the United Nations Charter.

The Court examined whether nuclear weapons were subject to a specific prohibition and whether their employment could comply with the general rules of humanitarian law. The absence of a comprehensive and universal prohibition under the law assessed in 1996 did not settle the question of legality.

5.1. The Court's Interpretation and Legal Conclusions

In paragraph 78, the Court identified two cardinal principles of international humanitarian law. The first concerns the protection of civilians and civilian objects through the distinction between military and civilian targets. The second prohibits causing unnecessary suffering to combatants, including through weapons that inflict harm exceeding what is unavoidable for legitimate military purposes.

The Court referred to the Martens Clause in connection with those principles. It observed that the clause had proved effective in addressing the rapid development of military technology. This reasoning confirmed that the application of humanitarian law is not confined to weapons existing when its principal treaties were negotiated (ICJ, 1996, para. 78).

Paragraph 84 addressed the relationship between Additional Protocol I and customary international law. The Court explained that rules already established as customary law remain binding independently of the Protocol, identifying the Martens Clause as an example. The observation supported its customary character without resolving the independent normative status of humanity and public conscience.

In paragraph 87, the Court reaffirmed the clause's continuing applicability and treated it as confirmation that the principles and rules of humanitarian law applied to nuclear weapons. The importance of that conclusion lay in rejecting the idea that technological novelty placed a weapon beyond established legal restrictions.

The Court did not derive an independent categorical prohibition of nuclear weapons from the Martens Clause. Its assessment remained connected to the applicable rules of humanitarian law, the United Nations Charter, and the characteristics and circumstances of nuclear-weapons use.

In operative paragraph 105(2)(E), the Court concluded, by seven votes to seven and the President's casting vote, that the threat or use of nuclear weapons would generally be contrary to the rules of international law applicable in armed conflict, particularly humanitarian law. It nevertheless could not reach a definitive conclusion concerning legality or illegality in an extreme circumstance of self-defense involving the very survival of a state.

That conclusion did not establish an exception to international humanitarian law. The Court identified an unresolved question in light of the international law and factual material before it. Its inability to reach a definitive answer cannot be interpreted as permission to disregard established humanitarian obligations whenever a state claims that its survival is threatened.

The legal position concerning nuclear weapons has also developed since 1996. The Treaty on the Prohibition of Nuclear Weapons, adopted on July 7, 2017, and in force since January 22, 2021, establishes express prohibitions on activities involving nuclear weapons for its parties, including their use and threat of use.

The Treaty does not impose its treaty obligations on every state regardless of participation. The existence of that later instrument must be distinguished from the legal position examined by the ICJ in 1996 and from the continuing customary-law questions concerning states not party to it.

The Court's reasoning on the Martens Clause remains relevant despite these subsequent developments. Its significance is not confined to the absence of a nuclear-weapons treaty prohibition at the time, but extends to the continuing application of established humanitarian law to weapons whose characteristics were not expressly contemplated by earlier instruments.

5.2. State Positions and Separate Judicial Opinions

The proceedings revealed substantial disagreement among states over the normative consequences of the Martens Clause. Several governments invoked humanity and public conscience when arguing that nuclear weapons were incompatible with international humanitarian law because of their destructive effects on civilians, combatants, and the environment.

Other states accepted that humanitarian law governed nuclear weapons while rejecting the proposition that the clause independently established their illegality. The United Kingdom argued that the clause did not itself create a prohibition and that the relevant legal restriction had to be identified through applicable international law.

The Russian Federation advanced a particularly restrictive position, questioning the clause's continuing practical relevance in light of the development of detailed humanitarian treaties. The Court's subsequent recognition of its continued applicability did not accept that the clause had become obsolete.

The individual judicial opinions demonstrate the importance of distinguishing the Court's conclusions from the reasoning advanced by particular judges.

Judge Mohamed Shahabuddeen developed an expansive interpretation in his dissenting opinion. He questioned whether a clause recognized as customary law could possess normative status while doing nothing beyond referring to obligations that existed independently of it.

In his analysis, the Martens Clause provided authority for treating humanity and public conscience as principles of international law whose practical content could be identified in light of changing circumstances. He regarded the views of states as relevant to determining the condition of public conscience without necessarily requiring the separate establishment of opinio juris for each resulting standard.

Judge Christopher Weeramantry also emphasized the independent significance of humanitarian principles. His dissent considered the clause within a broader examination of the humanitarian consequences of nuclear weapons, the protection of civilians, and the relationship between established legal restrictions and public conscience.

These interpretations supported stronger conclusions concerning the illegality of nuclear weapons than the Court was prepared to adopt. They remain significant contributions to the doctrinal debate, but their reasoning cannot be attributed to the Court as a whole.

The 1996 Advisory Opinion consequently established two important propositions without resolving the entire controversy. International humanitarian law applies to nuclear weapons, and the Martens Clause retains its legal relevance. Whether humanity and public conscience independently establish additional prohibitions remained disputed.

The distinction also illustrates the significance of ICJ advisory opinions. Although they are not binding judgments between parties in contentious proceedings, advisory opinions carry substantial judicial authority. Their interpretation requires careful separation of the Court's conclusions, supporting reasoning, and individual judicial opinions.

6. The Martens Clause in International Criminal Jurisprudence

International criminal proceedings have repeatedly invoked the Martens Clause when interpreting humanitarian obligations. These references demonstrate its judicial relevance, although they have not consistently established independent rules of responsibility derived directly from the clause.

An important early example appears in the Krupp judgment of July 31, 1948, delivered by a United States Military Tribunal at Nuremberg. The proceedings concerned, among other matters, the exploitation of property in occupied territories and violations of the laws and customs of war.

The Tribunal described the Martens Clause as more than a merely aspirational declaration and recognized its potential significance where particular circumstances were not expressly governed by the Hague Regulations. Its discussion suggested that humanitarian considerations could provide a relevant legal standard.

The Tribunal nevertheless resolved the questions concerning plunder and spoliation by applying established provisions of the Hague Regulations. Its conclusions rested on the rules governing occupation and the protection of property rather than an independently established prohibition derived from the Martens Clause.

The distinction is evident in the Tribunal's own reasoning, as reproduced in Volume X of the United Nations War Crimes Commission's Law Reports of Trials of War Criminals. After discussing the clause, the Tribunal considered the applicable Hague provisions sufficiently clear to determine the issues before it (United Nations War Crimes Commission, 1949, pp. 133–134).

The International Criminal Tribunal for the former Yugoslavia subsequently referred to the clause in Prosecutor v. Martić, Case No. IT-95-11-R61, in a decision of March 8, 1996. The proceedings arose from attacks against civilians in Zagreb and concerned the review of an indictment under Rule 61 of the Tribunal's Rules of Procedure and Evidence.

The Trial Chamber invoked the clause in connection with the prohibition of attacks against civilians and the principle that belligerents do not enjoy an unlimited choice of means and methods of warfare. Its reasoning reinforced established humanitarian restrictions rather than conclusively establishing a separate prohibition based exclusively on public conscience.

The procedural status of the decision limits the conclusions that may be drawn from it. A Rule 61 review was not a final trial judgment determining individual criminal responsibility after full evidentiary proceedings. The reference to the Martens Clause remains relevant judicial reasoning, but should not be presented as a final merits holding creating an autonomous humanitarian-law prohibition.

A more extensive discussion appeared in the ICTY Trial Chamber judgment of January 14, 2000, in Prosecutor v. Kupreškić et al., Case No. IT-95-16-T. The proceedings concerned crimes committed during attacks on the village of Ahmići in central Bosnia in April 1993.

In paragraph 525, the Trial Chamber recognized the customary status of the Martens Clause while rejecting the proposition that humanity and public conscience had become independent sources of international law. It nevertheless considered those principles relevant to interpreting humanitarian rules when their precise scope was uncertain.

Paragraph 526 developed this approach in relation to civilian protection. The Chamber suggested that repeated attacks against military objectives, each causing incidental civilian harm, might require consideration of their cumulative consequences when determining whether a pattern of military conduct complied with humanitarian obligations.

The argument concerned circumstances where individual attacks occupied an uncertain area between clear legality and illegality. It was not a general conclusion that the accumulation of independently lawful attacks automatically constituted a violation of international humanitarian law.

A subsequent committee established to advise the ICTY Prosecutor on NATO's bombing campaign against the Federal Republic of Yugoslavia examined the Chamber's reasoning. In its Final Report, paragraph 52, the committee characterized the cumulative-effects formulation as progressive and ambiguous in practical application.

The committee rejected the proposition that the mere accumulation of individually lawful attacks necessarily constituted a crime. Its assessment was an institutional evaluation prepared for the Prosecutor, not a binding judgment of an ICTY Trial or Appeals Chamber.

Paragraph 527 of Kupreškić raised a distinct and more controversial issue concerning customary-law formation. In discussing reprisals against civilians, the Trial Chamber suggested that opinio juris might assume greater significance than consistent state practice under the influence of the Martens Clause.

That proposition reflects an expansive interpretation of the clause's relationship to customary international law. It should not be confused with the more widely accepted proposition that humanitarian principles may inform the interpretation of established obligations. The ordinary method of identifying customary law continues to require consideration of general practice and acceptance as law.

The subsequent procedural history also requires qualification. On October 23, 2001, the ICTY Appeals Chamber reversed the convictions of Zoran, Mirjan, and Vlatko Kupreškić.

It partially allowed the appeals of Drago Josipović and Vladimir Šantić, reducing their sentences while maintaining important findings of criminal responsibility and entering additional convictions on the prosecution's appeal concerning cumulative convictions.

The reversal of particular convictions does not itself establish that every general legal proposition expressed in the Trial Judgment was rejected. Equally, the Trial Chamber's broader observations on the Martens Clause should not be represented as having received unqualified appellate endorsement.

The principle of legality imposes an additional limit on expansive reliance upon humanitarian principles in criminal proceedings. Individual criminal responsibility requires a sufficiently established prohibition and an ascertainable legal basis for liability. The seriousness of an alleged humanitarian violation cannot replace the legal elements necessary to establish an international crime.

Judicial treatment of the Martens Clause consequently demonstrates its interpretative significance more clearly than any autonomous capacity to establish criminal offenses. Tribunals have invoked it to reinforce humanitarian protection, but the determination of criminal responsibility remains dependent on applicable legal rules and the requirements of the relevant offense.

7. Application to Emerging Means and Methods of Warfare

The Martens Clause retains practical significance because military technologies can develop more rapidly than international agreements specifically regulating their use. Existing humanitarian treaties were drafted in particular historical circumstances, often before contemporary targeting systems, autonomous weapons, and other advanced military capabilities became technically possible.

The absence of a treaty devoted to a particular technology does not place that technology outside international humanitarian law. General restrictions on the conduct of hostilities remain applicable, including the principles of distinction, proportionality, precautions, and the prohibition of unnecessary suffering.

The legal assessment must distinguish the characteristics of a weapon from the circumstances of its employment. A weapon may be prohibited by its nature, while another may be capable of lawful use but employed unlawfully in a particular operation. The Martens Clause does not remove that distinction.

For example, the absence of a treaty expressly prohibiting a particular targeting technology would not resolve whether its use complies with distinction. That inquiry would depend on whether the circumstances of its employment permit lawful military objectives to be distinguished from civilians and civilian objects.

The same reasoning applies to proportionality and precautions. A weapon's novelty does not displace the obligation to assess expected incidental civilian harm or implement feasible measures to reduce it. The applicable rules must be interpreted according to their established legal content and the circumstances of the proposed operation.

The ICRC's 2025 Commentary identifies the continued applicability of humanitarian rules to technological developments as an important function of the clause. This interpretation is consistent with the ICJ's treatment of nuclear weapons and supports the application of existing rules to new military capabilities without assuming that technological novelty independently establishes illegality (ICRC, 2025, para. 7044).

7.1. Autonomous Weapons and the Principles of Humanity

Autonomous weapon systems raise difficult legal questions because they may select and engage targets after activation without further human intervention. Their characteristics vary considerably, and the legal implications depend on the system's capabilities, operational environment, foreseeable effects, and the decisions governing its deployment.

A central concern is whether the use of such systems allows compliance with the rules governing the conduct of hostilities. These include the obligation to distinguish lawful military objectives from protected persons and objects, the prohibition of disproportionate attacks, and the requirement to take feasible precautions.

The ICRC's 2026 position paper, Autonomous Weapon Systems and International Humanitarian Law: Selected Issues, emphasizes that existing humanitarian obligations remain applicable to autonomous weapons. It also identifies the difficulty of anticipating and limiting a system's effects as a significant legal and humanitarian concern.

The paper distinguishes the obligations of human decision-makers from the technical functions performed by a weapon system. International humanitarian law binds the persons and parties responsible for military operations. A machine's ability to perform targeting functions does not transfer legal responsibility away from those who develop, authorize, or employ it.

Debates concerning autonomous weapons and international law also address whether decisions involving lethal force should remain subject to particular forms of human judgment or control. The principles of humanity and public conscience frequently appear in arguments concerning the delegation of targeting functions to machines.

These arguments raise questions extending beyond the application of existing targeting rules. Some concern the consequences of reduced human control for compliance with humanitarian law. Others involve ethical objections to allowing machines to select and engage human targets, even where particular technical applications might satisfy existing legal restrictions.

The distinction between these concerns is essential. A humanitarian or ethical objection may support the adoption of additional legal restrictions without establishing that a particular system is already prohibited under customary international law.

The ICRC has called for new legally binding international rules addressing autonomous weapons, including prohibitions and restrictions on certain systems. Its 2026 position recognizes that existing humanitarian law applies while maintaining that additional regulation is needed to address legal uncertainty and broader humanitarian concerns.

Those proposals do not themselves constitute universally binding treaty obligations. Their legal status depends on the development and adoption of applicable international rules.

The Martens Clause remains relevant to this debate because it affirms the continuing protection of persons affected by warfare and may inform the interpretation of established obligations. It does not independently determine that every autonomous weapon system is unlawful.

7.2. Weapons Reviews and the Limits of Legal Prohibition

Article 36 of Additional Protocol I establishes a specific obligation concerning the legal review of new weapons, means, and methods of warfare. High Contracting Parties must determine, during the study, development, acquisition, or adoption of a new weapon or method, whether its employment would be prohibited in some or all circumstances by the Protocol or another applicable rule of international law.

The obligation requires an assessment of applicable law rather than a search limited to treaties expressly naming the weapon. General humanitarian rules may restrict a technology even where no dedicated international agreement governs its development or use.

A legal review must consider the weapon's relevant characteristics and the circumstances in which it is expected to be employed. These may include its foreseeable effects, the degree of control available to those using it, and whether its operation permits compliance with applicable restrictions on targeting and unnecessary suffering.

The obligation under Article 36 is a treaty requirement for states party to Additional Protocol I. It should not be described as an identical treaty obligation imposed on states that have not accepted the Protocol. Any separately claimed customary obligation concerning weapons reviews requires its own legal basis.

The Martens Clause may inform the review by directing attention to customary international humanitarian law and the continuing relevance of humanitarian principles. Its interpretative function is particularly useful where an existing rule must be applied to technological characteristics not anticipated when the rule was formulated.

Consider an autonomous targeting system intended for use in an environment containing both military personnel and civilians. The legal assessment would need to examine the system's ability to identify lawful targets, its operational restrictions, its foreseeable behavior, and the conditions under which human operators could lawfully authorize its employment.

If those conditions made compliance with distinction or other applicable obligations impossible, the system's use could be prohibited under established humanitarian rules. The prohibition would arise from the relevant legal obligation, not merely from the absence of a treaty specifically regulating autonomous weapons.

Where a technology could be employed lawfully in some circumstances but not others, the review would need to distinguish those circumstances. The conclusion might concern restrictions on particular uses rather than a categorical prohibition of the weapon itself.

The Martens Clause does not replace this legal assessment. It reinforces the need to examine the wider body of international humanitarian law and may guide interpretation where the application of existing obligations remains uncertain.

Its continuing relevance also extends to the development of international legal standards. Humanitarian concerns associated with new technologies may influence treaty negotiations, state practice, and legal interpretations. Such developments must nevertheless be distinguished from binding obligations already established under international law.

Conclusion

The Martens Clause preserves an important principle of international humanitarian law: the absence of an express treaty provision does not extinguish the international legal protection afforded to persons affected by armed conflict. Its recognition as customary international law confirms that humanitarian obligations cannot be reduced to the specific provisions of individual treaties.

The clause's precise normative consequences remain disputed. Its minimum legal effect is to preserve the continuing application of customary humanitarian law alongside treaty obligations and to prevent treaty silence from being treated as proof of unrestricted military freedom.

The more difficult question concerns whether the principles of humanity and the dictates of public conscience possess independent normative force. International jurisprudence recognizes their importance, particularly in the interpretation and application of humanitarian rules, but has not conclusively established that they constitute autonomous sources of generally applicable prohibitions.

The ICJ's 1996 Nuclear Weapons Advisory Opinion illustrates both the authority and the limits of the clause. The Court affirmed its continued applicability to weapons developed after earlier humanitarian treaties without treating it as an independent basis for a categorical nuclear-weapons prohibition. International criminal jurisprudence similarly demonstrates its interpretative significance while preserving the need to establish the legal rules governing individual responsibility.

Emerging military technologies make these distinctions increasingly relevant. The Martens Clause confirms that technological developments do not escape established humanitarian constraints merely because they were not anticipated by earlier treaty negotiations. Its function is to sustain the application of international law and inform the interpretation of humanitarian obligations, while leaving the establishment of particular prohibitions subject to the legal requirements governing their existence, scope, and enforcement.

References

Cassese, A. (2000) ‘The Martens Clause: Half a Loaf or Simply Pie in the Sky?’, European Journal of International Law, 11(1), pp. 187–216. Available at: https://doi.org/10.1093/ejil/11.1.187 (Accessed: 28 October 2026).

Convention on Prohibitions or Restrictions on the Use of Certain Conventional Weapons Which May Be Deemed to Be Excessively Injurious or to Have Indiscriminate Effects (1980) Adopted 10 October 1980, entered into force 2 December 1983, 1342 UNTS 137. Available at: https://ihl-databases.icrc.org/en/ihl-treaties/ccw-1980 (Accessed: 28 October 2026).

Geneva Convention (I) for the Amelioration of the Condition of the Wounded and Sick in Armed Forces in the Field (1949) Adopted 12 August 1949, entered into force 21 October 1950, 75 UNTS 31. Available at: https://ihl-databases.icrc.org/en/ihl-treaties/gci-1949 (Accessed: 28 October 2026).

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