War law is the body of international and domestic rules that governs how armed conflicts are fought and how people affected by war must be treated. It is commonly known as international humanitarian law (IHL) or the law of armed conflict (LOAC). These rules seek to reduce unnecessary suffering by protecting civilians, wounded and sick people, prisoners of war, and others who are not taking part in fighting.
War law does not make war legal or illegal by itself. Instead, it establishes rules for conduct during an armed conflict. For example, parties to a conflict must distinguish between military targets and civilians, must not intentionally attack protected persons, and must follow restrictions on certain weapons and methods of warfare.
What Does War Law Mean?
War law refers to legal rules that apply during armed conflicts. These rules regulate both the conduct of hostilities and the treatment of people affected by conflict.
The rules apply differently depending on the type of conflict. An international armed conflict generally involves two or more states, while a non-international armed conflict involves a state and an organized armed group, or qualifying armed groups fighting each other.
The central idea is that even during war, there are limits on what parties can do.
What Is the Purpose of War Law?
The main purpose of war law is to limit the human suffering caused by armed conflict.
It does this by establishing rules concerning:
- Protection of civilians
- Treatment of prisoners and detainees
- Protection of wounded and sick people
- Protection of medical personnel and facilities
- Conduct of military operations
- Choice and use of weapons
- Treatment of people in areas under occupation
- Protection of certain cultural and humanitarian objects
War law does not require soldiers to stop fighting. Instead, it places legal limits on how fighting may be conducted.
What Are the Main Principles of War Law?
Several fundamental principles guide the conduct of hostilities.
1. Distinction
Parties to a conflict must distinguish between military objectives and civilians.
Military operations may generally be directed against lawful military objectives, but civilians and civilian objects cannot be intentionally targeted simply because a war is taking place.
2. Proportionality
An attack against a lawful military objective can still be unlawful if the expected incidental harm to civilians would be excessive in relation to the concrete and direct military advantage anticipated.
Proportionality does not mean that civilian casualties automatically make an attack illegal. The circumstances and expected effects of the attack matter.
3. Military Necessity
Military force must be connected to a legitimate military purpose. Military necessity does not permit actions that are otherwise prohibited by international humanitarian law.
4. Precautions in Attack
Those planning or carrying out attacks must take feasible precautions to avoid or minimize civilian harm.
This can include choosing appropriate targets, weapons, timing, or methods when reasonably possible.
5. Humanity
People who are not participating in hostilities, as well as those who are no longer taking part, must be treated humanely.
Torture, cruel treatment, and certain forms of humiliating or degrading treatment are prohibited.
Who Does War Law Protect?
War law provides protection to different categories of people depending on the circumstances.
Civilians
Civilians are generally protected from being directly targeted. Parties to a conflict must take steps to reduce civilian harm during military operations.
However, civilians may lose protection from direct attack for such time as, and to the extent that, they directly participate in hostilities under the applicable rules.
Wounded and Sick People
Wounded and sick members of armed forces who are no longer able to fight are entitled to protection and humane treatment.
They should receive appropriate medical care without unlawful discrimination.
Prisoners of War
In an international armed conflict, qualifying captured members of enemy armed forces may have prisoner-of-war status.
Prisoners of war must be treated humanely. They are protected against violence, intimidation, torture, and certain forms of humiliating or degrading treatment.
Medical Personnel and Facilities
Medical personnel, hospitals, ambulances, and other protected medical activities receive special protection under international humanitarian law, subject to the conditions established by the applicable rules.
What Is the Difference Between War Law and the Law About Starting a War?
This distinction is important.
War law, or IHL, primarily regulates conduct during armed conflict. It asks questions such as:
- Who may be attacked?
- What precautions must be taken?
- How must detainees be treated?
- What weapons or methods are prohibited?
- How must the wounded and sick be protected?
The separate body of international law concerning whether force may lawfully be used in the first place is commonly called jus ad bellum.
In simple terms:
Jus ad bellum concerns whether the use of force is lawful, while international humanitarian law regulates conduct once an armed conflict exists.
Does War Law Apply Only When Both Sides Follow It?
No.
The legal obligations of international humanitarian law do not disappear simply because one party violates the rules.
A party cannot generally justify its own unlawful conduct by claiming that the opposing side committed a violation first.
The rules are intended to apply to the parties to an armed conflict according to the applicable treaty and customary international law.
What Are War Crimes?
A war crime is a serious violation of international humanitarian law that may result in individual criminal responsibility under applicable international or domestic law.
Examples can include, depending on the circumstances and applicable law:
- Intentionally directing attacks against civilians
- Torturing protected persons
- Intentionally killing protected persons
- Taking hostages
- Certain unlawful attacks
- Certain forms of cruel or inhuman treatment
- Certain serious violations involving prisoners of war
Not every violation of the laws of war automatically constitutes a war crime. Whether conduct amounts to a war crime depends on the applicable law and the specific facts.
What Are the Geneva Conventions?
The four Geneva Conventions of 1949 are among the most important treaties in international humanitarian law.
They establish protections for:
- Wounded and sick members of armed forces on land
- Wounded, sick, and shipwrecked members of armed forces at sea
- Prisoners of war
- Civilians during wartime
The Geneva Conventions are supplemented by additional treaties and customary international law.
The United States is a party to the four 1949 Geneva Conventions.
What Is Common Article 3?
Common Article 3 appears in all four Geneva Conventions.
It establishes minimum humanitarian protections for certain persons taking no active part in hostilities in a non-international armed conflict.
Among other protections, it prohibits:
- Violence to life and person
- Murder
- Mutilation
- Cruel treatment
- Torture
- Taking of hostages
- Humiliating and degrading treatment
- Certain forms of punishment without a properly constituted court
Common Article 3 is particularly important because it provides basic protections in conflicts that are not necessarily fought between two states.
What Laws Govern War in the United States?
The United States follows international humanitarian law through a combination of international treaties, customary international law, federal statutes, executive and military rules, and Department of Defense guidance.
Important sources include the Geneva Conventions, applicable additional treaties, federal criminal laws, and military law.
War Crimes Act — 18 U.S.C. § 2441
The War Crimes Act, codified at 18 U.S.C. § 2441, establishes federal criminal offenses for certain war crimes.
Its application depends on the conduct, the protected status of the victims, the circumstances, and the jurisdictional requirements established by the statute.
Therefore, it is more accurate to say that the War Crimes Act criminalizes specified conduct that falls within the statute rather than saying that every violation of every rule of war is automatically prosecuted under this law.
Uniform Code of Military Justice
The Uniform Code of Military Justice (UCMJ) provides the military justice system applicable to members of the U.S. armed forces.
Military personnel can face disciplinary or criminal proceedings for conduct that violates applicable military law, including offenses connected with unlawful conduct during armed conflict.
Department of Defense Law of War Manual
The Department of Defense Law of War Manual provides detailed guidance concerning the Department of Defense’s interpretation and application of the law of war.
It addresses subjects such as targeting, protected persons, detention, treatment of detainees, weapons, and military operations.
Are All Weapons Banned by War Law?
No.
International humanitarian law does not prohibit every weapon used in warfare. Instead, it regulates weapons according to applicable treaties and customary international law.
Some weapons are subject to specific prohibitions or restrictions. For example, international treaties prohibit or restrict the use of certain chemical and biological weapons.
Weapons may also be unlawful because their use in a particular manner violates general principles of humanitarian law.
The legality of a weapon can therefore depend on both the weapon itself and the way it is used.
Can a Military Attack Be Legal Even If Civilians Are Killed?
Potentially, yes.
International humanitarian law does not establish a rule that every civilian death automatically makes an attack unlawful.
An attack must comply with applicable rules, including distinction, proportionality, and precautions.
For example, an attack directed at a lawful military objective may result in incidental civilian casualties. The legality can depend on factors such as what was known or reasonably expected when the attack was planned, the anticipated military advantage, the expected civilian harm, and the precautions taken.
An attack intentionally directed against civilians is fundamentally different from incidental civilian harm arising during a lawful attack.
What Happens When War Law Is Violated?
Consequences depend on the nature of the violation and the applicable legal system.
Possible consequences can include:
- Criminal investigation
- Military disciplinary proceedings
- Domestic criminal prosecution
- Prosecution for war crimes
- Command investigations
- International proceedings where jurisdiction exists
- Other legal or disciplinary measures
Individual responsibility can arise for people who personally commit prohibited acts and, under applicable rules, for certain forms of ordering, assisting, or otherwise contributing to unlawful conduct.
Does War Law Apply to Soldiers?
Yes.
Soldiers and other members of armed forces remain subject to the applicable laws of armed conflict.
Military training commonly includes instruction on the law of war, including rules concerning targeting, treatment of detainees, protection of civilians, and the handling of wounded and sick persons.
Military orders do not automatically make an otherwise unlawful act lawful.
Does War Law Apply to Non-State Armed Groups?
It can.
International humanitarian law can apply to qualifying armed groups involved in a non-international armed conflict.
The fact that an armed group is not a state does not mean that its members can ignore applicable humanitarian rules.
The precise legal obligations depend on the nature of the conflict, applicable treaties, customary international law, and other relevant legal rules.
What Is the Role of the Red Cross in War Law?
The International Committee of the Red Cross (ICRC) plays an important humanitarian role in armed conflicts.
Its work includes promoting respect for international humanitarian law, visiting certain detainees, assisting people affected by armed conflict, and helping clarify and develop understanding of humanitarian rules.
The ICRC is not a court that decides whether an individual committed a war crime.
What Does “Hors de Combat” Mean?
The French term hors de combat generally refers to a person who is out of the fight.
For example, a combatant may be hors de combat because they have been wounded, captured, or are otherwise placed outside the hostilities under applicable rules.
A person who is hors de combat must not be made the object of attack when protected by the applicable law and must be treated humanely.
Why Is War Law Important?
War law recognizes that armed conflict can cause enormous human suffering but establishes legal limits intended to preserve a basic level of humanity.
Its rules can help protect people who are not fighting and those who can no longer fight. They also provide legal standards for military operations, detention, medical treatment, and the use of weapons.
The existence of these rules does not prevent every violation. Their purpose is to establish obligations that parties to armed conflicts are legally required to respect.
Key Takeaways
- War law is commonly associated with international humanitarian law and the law of armed conflict.
- It regulates the conduct of parties during armed conflicts.
- Civilians are generally protected from direct attack.
- Wounded, sick, captured, and other protected persons must be treated humanely.
- The principles of distinction, proportionality, military necessity, precautions, and humanity are central to the conduct of hostilities.
- The Geneva Conventions of 1949 are foundational treaties of modern international humanitarian law.
- Some serious violations can constitute war crimes.
- U.S. law implements and enforces applicable rules through federal statutes, military law, and other legal authorities.
- The War Crimes Act is codified at 18 U.S.C. § 2441.
- The law of armed conflict is different from the international rules governing whether a state may lawfully resort to force.
Conclusion
War law establishes legal boundaries for armed conflict. Rather than allowing anything simply because a war is taking place, international humanitarian law requires parties to follow rules designed to protect civilians, detainees, wounded and sick people, and others who are not participating in hostilities.
For the United States, these obligations come from international treaties, customary international law, federal statutes, military law, and Department of Defense rules and guidance. Serious violations can lead to investigations, disciplinary action, or criminal prosecution where the applicable law provides for it.
Understanding war law is therefore important not only for military personnel but also for understanding how international law attempts to protect human life during armed conflict.
Frequently Asked Questions
Is war law legally binding?
Yes. Applicable rules of international humanitarian law are legally binding on the parties to an armed conflict. The exact rules that apply depend on the type of conflict and the relevant treaties and customary international law.
Can a prisoner of war be forced to provide military information?
A prisoner of war has specific protections under the Third Geneva Convention. The rules governing questioning and treatment of POWs limit what detaining authorities may lawfully do.
Are journalists protected during armed conflict?
Journalists who are civilians generally receive the protections afforded to civilians under international humanitarian law, provided they are not taking direct part in hostilities. Certain journalists accompanying armed forces may have different legal status under applicable rules.
What happens to property during an armed conflict?
International humanitarian law places restrictions on the destruction, seizure, and appropriation of property. The legality can depend on factors such as military necessity, whether the property is civilian or military, and whether an area is occupied.
Does war law protect cultural property?
Yes. International law provides special protection for certain cultural property, including important historical and cultural sites, subject to the applicable treaties and circumstances.
Can humanitarian organizations operate during a war?
Humanitarian organizations may operate during armed conflicts subject to applicable law, security conditions, and the consent or arrangements required in particular circumstances. International humanitarian law contains rules concerning humanitarian relief and access.
What is the difference between a war crime and a crime against humanity?
They are different categories of international crimes. A war crime is generally connected to an armed conflict and involves conduct prohibited by the applicable law of armed conflict. Crimes against humanity involve certain widespread or systematic attacks directed against a civilian population and do not require the same connection to an armed conflict.
Does international humanitarian law apply at sea?
Yes. International humanitarian law contains rules governing armed conflict at sea, including protections for wounded, sick, and shipwrecked persons and rules concerning naval warfare.
Who can investigate alleged war crimes?
Depending on the circumstances, investigations may be conducted by national authorities, military authorities, or other institutions with appropriate jurisdiction. International courts or tribunals may also have jurisdiction in particular situations.
Can a commander be responsible for crimes committed by subordinates?
Potentially. International law recognizes forms of responsibility involving commanders and superiors under specified circumstances. Whether responsibility exists depends on the applicable legal standard and the facts of the case.
Is there a single “War Law” in the United States?
No. There is not one comprehensive U.S. statute called the “War Law.” The legal framework consists of multiple sources, including international agreements, customary international law, federal statutes, military law, executive authorities, and Department of Defense rules and guidance.
Sources & References
- U.S. Department of Defense – Law of War Manual: https://dod.defense.gov
- International Committee of the Red Cross (ICRC) – Geneva Conventions: https://www.icrc.org/en/war-and-law/treaties-customary-law/geneva-conventions
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Prabh Kalsi is the founder and publisher of Law Act. He manages the website’s content research, organization, editing, and publishing. Law Act’s legal content is developed using publicly available legislation, government resources, official publications, and other authoritative sources. The website provides general legal information for educational and informational purposes and does not provide personalized legal advice.