1. Introduction.
International Humanitarian Law (IHL), also known as the law of armed conflict, regulates the conduct of hostilities during armed conflict. Its primary purpose is to limit human suffering while balancing military necessity with humanitarian considerations. The legal framework governing means and methods of warfare is primarily derived from the Geneva Conventions and their Additional Protocols.¹ These instruments establish limits on the choice of weapons and tactics available to belligerents. A key distinction is drawn between means of warfare (weapons and equipment) and methods of warfare (tactics and operational strategies).
2. Legal Framework.
2.1. Treaty Law.
The central treaty governing conduct of hostilities is Additional Protocol I to the Geneva Conventions. Article 35(1) explicitly provides that the right of parties to choose methods or means of warfare is not unlimited. This principle is foundational to modern IHL and restricts the use of weapons and tactics that cause unnecessary suffering or indiscriminate harm.²
2.2 Customary International Law.
Customary IHL binds all states regardless of treaty ratification. The International Committee of the Red Cross (ICRC) has identified customary rules that govern distinction, proportionality, and unnecessary suffering.³
3. Core Principles Governing Warfare.
The conduct of hostilities in International Humanitarian Law (IHL) is structured around four foundational principles: distinction, proportionality, military necessity, and humanity. These principles are not abstract ideas; they operate as binding legal rules under treaty law and customary international law, shaping how armed forces plan and execute military operations.
3.1 Principle of Distinction.
The principle of distinction is the cornerstone of IHL. It requires all parties to an armed conflict to distinguish at all times between civilians and combatants, and between civilian objects and military objectives. This principle is codified in Article 48 of Additional Protocol I, which imposes a general obligation on parties to direct operations only against military targets. It is also recognized as a rule of customary international law applicable in both international and non-international armed conflicts.⁴
The principle contains two core obligations:
★ Distinction between persons.
Combatants may be lawfully targeted. Civilians are protected from direct attack unless and for such time as they take a direct part in hostilities.
★ Distinction between objects.
Military objectives (e.g., weapons depots, command centres) may be targeted. Civilian objects (homes, schools, hospitals) are protected unless they become military objectives.
3.2 Principle of Proportionality.
The principle of proportionality prohibits attacks in which the expected incidental civilian harm would be excessive in relation to the anticipated military advantage. This principle is codified in Article 51(5)(b) of Additional Protocol I. It reflects a balancing mechanism between military necessity and humanitarian protection.⁵
3.3 Principle of Military Necessity.
Military necessity permits only those measures that are necessary to achieve a legitimate military objective and are not otherwise prohibited by international law. This principle does not grant unlimited freedom. Instead, it restricts force to what is Necessary, Proportionate and Legally permitted. Military necessity is not always codified in a single article but is embedded throughout IHL treaties and customary law. It is often interpreted alongside humanity to ensure balance. The ICJ in the Nuclear Weapons Advisory Opinion confirmed that humanitarian principles apply even in extreme security circumstances, indicating that necessity alone cannot justify unlawful means.⁶
3.4 Principle of Humanity.
The principle of humanity prohibits weapons and methods of warfare that cause superfluous injury or unnecessary suffering.This principle is explicitly stated in Article 35(2) of Additional Protocol I. It is also reflected in early Hague Law and customary international law.⁷
In armed conflict, there are limits on the level of suffering that can be legally inflicted. The law does not allow:
★ Weapons that worsen suffering without military advantage.
★ Methods that increase human pain beyond what is necessary to disable an enemy.
This principle is the foundation for banning or restricting Chemical and biological weapons, Blinding laser weapons, and Certain expanding or fragmenting ammunition. The ICJ in the Nuclear Weapons Advisory Opinion reaffirmed that methods of warfare must comply with “elementary considerations of humanity,” even where no specific treaty prohibition exists.⁸
4. Categories of Restricted or Prohibited Means of Warfare.
4.1. Chemical and Biological Weapons.
4.2. Nuclear Weapons.
The legal regime governing nuclear weapons is complex and remains unsettled in certain respects. There is no comprehensive treaty universally prohibiting their possession or use. However, their employment is constrained by fundamental principles of IHL, particularly distinction, proportionality, and the prohibition of unnecessary suffering. In its landmark Advisory Opinion on the Legality of the Threat or Use of Nuclear Weapons (1996), the International Court of Justice (ICJ) concluded that the use of nuclear weapons would generally be contrary to international humanitarian law, although it could not definitively determine legality in extreme circumstances of self-defense.¹² More recently, the Treaty on the Prohibition of Nuclear Weapons 2017 (TPNW) prohibits the development, possession, and use of nuclear weapons for its States Parties.¹³ Nevertheless, major nuclear-armed states have not ratified this treaty, leaving the regulation of nuclear weapons largely dependent on customary international law and general IHL principles.
4.3. Conventional Weapons with Excessive Harm.
Conventional weapons, including firearms, artillery, mines, and incendiary devices, are not inherently unlawful. However, certain categories are restricted when they cause unnecessary suffering or have indiscriminate effects. The Convention on Certain Conventional Weapons 1980 (CCW) provides a framework regulating specific types of conventional weapons deemed excessively injurious, including booby traps and incendiary weapons.¹⁴ Furthermore, the Ottawa Convention 1997 prohibits anti-personnel landmines due to their long-lasting humanitarian impact, particularly on civilians after the cessation of hostilities.¹⁵ These instruments reflect the principle that the choice of weapons is not unlimited and must conform to the requirements of distinction and proportionality. Customary international law reinforces these prohibitions by outlawing indiscriminate attacks and weapons that cannot be directed at a specific military objective.¹⁶
4.4. Obligation to Review New Weapons.
A critical preventive mechanism in IHL is the obligation of States to assess the legality of new weapons prior to their deployment. Article 36 of Additional Protocol I to the Geneva Conventions (1977) requires States to determine whether the use of a new weapon would be prohibited under international law in all or certain circumstances.¹⁷ This includes evaluation against criteria such as unnecessary suffering, indiscriminate effects, and environmental damage. The obligation is particularly significant in the context of rapidly evolving military technologies, including autonomous weapons and cyber capabilities. Although implementation varies among States, Article 36 is widely recognized as a binding treaty obligation for parties to Additional Protocol I and reflects a broader preventive norm under customary international law.¹⁸
4.5. Emerging Issues in Means of Warfare
Contemporary armed conflict increasingly involves technologies that challenge existing legal frameworks. Autonomous weapon systems (AWS), capable of selecting and engaging targets without direct human intervention, raise significant legal and ethical concerns regarding compliance with distinction and proportionality. Similarly, cyber warfare introduces new forms of attack targeting critical infrastructure such as hospitals, communication systems, and energy grids, raising questions about their classification under IHL. Artificial intelligence further complicates accountability and decision-making in targeting processes. While no comprehensive treaty governs these technologies, they remain subject to general principles of IHL and are actively discussed within the Convention on Certain Conventional Weapons (CCW) Group of Governmental Experts and the International Committee of the Red Cross.¹⁹
5. Methods of Warfare.
In International Humanitarian Law (IHL), “methods of warfare” refer to the tactics and ways in which armed forces conduct hostilities, as distinct from “means of warfare,” which are the weapons used. Methods of warfare regulate how attacks are carried out, including targeting practices, deception, siege tactics, and strategies that affect civilians and combatants during armed conflict. The law does not prohibit warfare itself but places strict limits on methods that violate humanitarian principles such as distinction, proportionality, military necessity, and humanity.²⁰
5.1. Principle of Distinction and Targeting Methods.
One of the most fundamental rules governing methods of warfare is the obligation to distinguish at all times between civilians and combatants and between civilian objects and military objectives. This principle directly regulates targeting methods used in combat operations. Parties to a conflict must ensure that attacks are directed only at legitimate military targets and not at civilian populations or infrastructure.²¹ Methods of warfare such as indiscriminate shelling, area bombardment in populated zones, or attacks without proper target verification violate this principle. The International Committee of the Red Cross (ICRC) confirms that distinction is a cornerstone of customary international law binding on all states.²²
5.2. Prohibition of Indiscriminate Attacks.
Methods of warfare that cannot be directed at a specific military objective or that affect military targets and civilians without distinction are strictly prohibited. Indiscriminate attacks include the use of methods that strike military and civilian objects without discrimination or that employ means incapable of limited targeting.²³ This includes, for example, blanket bombing of urban areas or firing weapons into densely populated zones without precise targeting capability. International law treats such conduct as a serious violation of IHL and, in some cases, a war crime under international criminal law.
5.3. Principle of Proportionality in Attack Methods.
Even when targeting a legitimate military objective, the method of attack must comply with the principle of proportionality. This means that incidental civilian harm must not be excessive in relation to the concrete and direct military advantage anticipated.²⁴ Methods such as repeated bombardment of mixed civilian-military areas or use of heavy explosive force in populated zones are assessed under this rule. Proportionality does not prohibit all civilian harm but imposes a strict legal balancing test on commanders before launching an attack.
5.4. Prohibition of Perfidy and Requirement of Good Faith.
International law also regulates deceptive methods of warfare. While certain forms of deception (such as camouflage, decoys, and misinformation) are lawful, perfidy is strictly prohibited. Perfidy refers to acts that invite the confidence of an adversary to lead them to believe they are entitled to protection under IHL, with the intent to betray that confidence.²⁵ Examples include pretending to surrender or feigning civilian status to attack the enemy. Such methods are considered unlawful because they undermine trust in humanitarian protections and endanger civilians and wounded combatants.
5.5. Siege Warfare and Starvation as a Method.
Siege warfare is a traditional method of warfare that remains legally regulated. While encirclement of military forces is not prohibited, international law strictly forbids using starvation of civilians as a method of warfare.²⁶ Parties to conflict must allow the passage of humanitarian relief essential for civilian survival, subject to control measures. The prohibition of starvation reflects the broader humanitarian principle that civilians must never be used as instruments of war.
5.6. Methods Affecting the Environment.
Modern IHL also restricts methods of warfare that cause severe environmental damage. Methods intended or expected to cause widespread, long-term, and severe damage to the natural environment are prohibited.²⁷ This includes tactics such as environmental destruction to deny territory use, pollution of water sources, or burning of agricultural land on a massive scale. Environmental protection in warfare is increasingly recognized as part of customary international law and linked to civilian survival.
5.7. Terror and Psychological Warfare Methods.
Methods of warfare designed primarily to spread terror among the civilian population are prohibited. International law explicitly forbids acts or threats of violence whose primary purpose is to terrorize civilians.²⁸ This includes attacks on civilian areas intended to cause fear rather than achieve a concrete military objective. Psychological warfare itself is not entirely illegal, but it becomes unlawful when it violates civilian protections or involves prohibited threats or acts of violence.
5.8. Hostage-Taking and Human Shields.
Certain coercive methods of warfare are absolutely prohibited, including hostage-taking and the use of human shields. Hostage-taking involves seizing individuals to compel actions by the opposing party, while human shields involve using civilians to render military objectives immune from attack. Both practices violate fundamental principles of humanity and are considered serious breaches of IHL and war crimes under international law.²⁹
References:
1. Geneva Conventions 1949.
2. Additional Protocol I to the Geneva Conventions (1977) art 35(1).
3. International Committee of the Red Cross, Customary International Humanitarian Law (CUP 2005).
4. Additional Protocol I (n 2) art 48.
5. ibid art 51(5)(b).
6. Legality of the Threat or Use of Nuclear Weapons Advisory Opinion [1996] ICJ Rep 226.
7. ibid art 35(2).
8. Legality of the Threat or Use of Nuclear Weapons Advisory Opinion [1996] ICJ Rep 226.
9. Chemical Weapons Convention 1993, arts I–IV.
10. Biological Weapons Convention 1972, arts I–II.
11. International Committee of the Red Cross (ICRC), Customary International Humanitarian Law Study (2005) rules 73–74.
12. Legality of the Threat or Use of Nuclear Weapons (Advisory Opinion) [1996] ICJ Rep 226.
13. Treaty on the Prohibition of Nuclear Weapons 2017, arts 1–2.
14. Convention on Certain Conventional Weapons 1980.
15. Ottawa Convention on Anti-Personnel Mines 1997, arts 1–2.
16. ICRC (n 3) rules 70–83.
17. Protocol Additional to the Geneva Conventions (Protocol I) 1977, art 36.
18. ICRC, A Guide to the Legal Review of New Weapons, Means and Methods of Warfare (2006).
19. UN CCW Group of Governmental Experts on Lethal Autonomous Weapon Systems (ongoing reports, 2016–2023); ICRC, Autonomous Weapon Systems: Implications of Increasing Autonomy in the Critical Functions of Weapons (2016).
20. Geneva Conventions 1949; Additional Protocol I to the Geneva Conventions 1977, arts 48, 51.
21. Additional Protocol I 1977, art 48.
22. International Committee of the Red Cross (ICRC), Customary International Humanitarian Law (CUP 2005).
23. Additional Protocol I 1977, art 51(4).
24. Additional Protocol I 1977, art 51(5)(b).
25. Additional Protocol I 1977, art 37.
26. Additional Protocol I 1977, art 54.
27. Additional Protocol I 1977, art 35(3).
28. Additional Protocol I 1977, art 51(2).
29. Geneva Conventions 1949; Additional Protocol I 1977; ICRC, Customary International Humanitarian Law Study (2005) rules 96–97.
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