A war crime is a serious violation of international humanitarian law (IHL) committed in connection with an armed conflict. The category covers far more than attacks that kill civilians: it includes torture, hostage-taking, certain unlawful killings and transfers, intentionally attacking protected people or civilian objects, pillage, some forms of sexual violence, the recruitment or use of children in hostilities, and certain prohibited methods or means of warfare. But not every violation of the laws of war is automatically a war crime.
The legal analysis also depends on the type of conflict and the circumstances of the conduct. An attack that causes civilian deaths is not automatically a war crime, for example. Investigators must examine whether the target was lawful, what the attacker knew, what precautions were taken, whether the expected civilian harm was excessive compared with the anticipated military advantage, and whether the required mental element for the particular offense was present. International humanitarian law regulates how war is fought; it is distinct from the separate legal question of whether a state was entitled to start using force in the first place.
The legal starting point: international humanitarian law
International humanitarian law is the body of international rules designed to limit suffering during armed conflict.
Its principal sources include the four Geneva Conventions of 1949, their Additional Protocols, other treaties and customary international law. The rules protect people who are not, or are no longer, taking part in hostilities and restrict the weapons and methods that parties may use.
This produces an important distinction between two questions:
- Was the decision to use force lawful?
- Was the conduct of the war lawful once the conflict began?
IHL principally addresses the second question. Whether a state was legally entitled to use armed force in the first place is generally governed by the UN Charter and the separate law concerning the use of force, sometimes described as jus ad bellum.
A state cannot justify an unlawful attack during war by arguing that the other side also violated IHL. Each party remains bound by the rules.
What are the main categories of war crimes?
There is no single short list covering every legal system and every armed conflict. The Rome Statute of the International Criminal Court provides one of the most important codifications, while the Geneva Conventions, Additional Protocols and customary international law provide additional sources.
Among the conduct that can constitute war crimes are:
- Intentionally killing protected persons
- Torture and inhuman treatment
- Intentionally causing great suffering or serious injury
- Taking hostages
- Unlawful deportation, transfer or confinement
- Intentionally attacking civilians
- Intentionally attacking civilian objects
- Pillage
- Certain forms of sexual violence
- Using children under 15 to participate actively in hostilities
- Certain attacks against medical, humanitarian, religious, educational or cultural objects
- Using prohibited weapons or methods of warfare
- Attacking people who have surrendered or are otherwise hors de combat under circumstances prohibited by international law.
The precise list depends on whether the conflict is international or non-international and on the legal instrument being applied.
Deliberately attacking civilians
One of the clearest examples is deliberately directing an attack against civilians who are not taking direct part in hostilities.
Civilians enjoy protection from direct attack under IHL. The Rome Statute expressly identifies intentionally directing attacks against the civilian population or individual civilians not directly participating in hostilities as a war crime.
The key word is intentionally.
If a military force deliberately targets a civilian population, that is fundamentally different from an attack against a lawful military objective in which civilians are unintentionally harmed.
That distinction does not mean accidental civilian deaths are legally irrelevant. Other rules—particularly those governing proportionality and precautions—can make an attack unlawful even when civilians were not deliberately targeted.
Attacking civilian buildings
Civilian objects are also protected.
A building is generally a civilian object unless it qualifies as a military objective under the applicable rules.
The Rome Statute specifically identifies intentionally directing attacks against civilian objects as a war crime in international armed conflicts.
Schools, houses, shops and ordinary infrastructure do not become lawful targets simply because a war is taking place.
But the legal status of a particular building can change if it is being used for military purposes and meets the applicable definition of a military objective.
That is why investigators examining a strike on a school, for example, would need to establish not simply that the school was destroyed, but whether it was being used for military purposes, what the attacking force knew, and whether the attack complied with the other rules governing targeting.
Why civilian deaths do not automatically mean a war crime
This is one of the most important distinctions in the law of armed conflict.
Civilian casualties can occur during a lawful attack.
IHL requires parties to distinguish between civilians and combatants and between civilian objects and military objectives. It also prohibits attacks expected to cause incidental civilian harm that would be clearly excessive in relation to the concrete and direct military advantage anticipated. The attacker must also take feasible precautions to reduce civilian harm.
Consider a hypothetical attack on a legitimate military command post located near homes.
If the attacker reasonably identifies the building as a military objective, takes feasible precautions to protect civilians and determines that the expected civilian harm is not clearly excessive relative to the anticipated military advantage, civilian casualties do not automatically transform the attack into a war crime.
If, however, the attacker deliberately targets the homes, knowingly launches an attack whose expected civilian harm is clearly excessive, or fails to take required precautions, the legal analysis changes substantially.
The facts and information available to the attacker at the time of the decision are therefore critical.
The principle of distinction
The principle of distinction is one of the foundations of IHL.
Parties must distinguish between:
- Civilians and combatants
- Civilian objects and military objectives
Attacks may be directed only against legitimate military objectives.
This is why investigations into alleged unlawful attacks often focus on targeting intelligence, reconnaissance, communications, weapons capabilities and the information available to commanders before the attack.
A photograph showing a destroyed civilian building can establish that the building was damaged. It does not, by itself, establish why it was attacked or what the attacker knew.
Those additional questions are often decisive.
Proportionality is not the same as equal casualties
The proportionality rule is sometimes misunderstood as requiring roughly equal numbers of military and civilian casualties.
It does not.
The legal test concerns expected incidental civilian harm in relation to the concrete and direct military advantage anticipated.
The assessment is therefore not simply:
How many civilians died?
Investigators may instead need to ask:
What military advantage did the attacker anticipate, what civilian harm did it expect, and was that expected harm clearly excessive in relation to that advantage?
That can make proportionality legally and factually difficult to assess after an attack.
The analysis is generally concerned with the information reasonably available when the attack was planned or launched, rather than judging the decision solely with hindsight.
Precautions matter too
Even an attack against a legitimate military objective is subject to precautionary obligations.
Parties must take feasible measures to verify targets and minimize civilian harm. The precise requirements depend on the circumstances.
Possible precautions can include selecting a different weapon, changing the timing of an attack, issuing warnings where appropriate, choosing another method of attack or cancelling an attack when the legal requirements cannot be met.
This is why two attacks against apparently similar targets can produce different legal assessments.
The target alone does not determine whether an attack was lawful.
Torture is a war crime
Torture and cruel or inhuman treatment are prohibited.
The prohibition applies to people protected by IHL, including detainees and people who are no longer participating in hostilities. The Rome Statute expressly includes torture and inhuman treatment among war crimes.
The prohibition does not disappear because a detainee is suspected of terrorism, espionage or another serious offense.
A person who is detained during armed conflict remains protected by applicable international law.
Killing someone who has surrendered
A combatant who has surrendered or is otherwise hors de combat is protected from being deliberately attacked.
The Rome Statute includes killing or wounding a combatant who has laid down their arms or otherwise surrendered at discretion among the war crimes applicable to international armed conflicts.
The practical question can be complicated when battlefield circumstances are chaotic.
Investigators may need to establish whether the person had actually surrendered, whether the attacking force knew or should have known of the surrender, and what happened immediately before and after the death.
Again, the legal classification depends on evidence rather than the mere fact that someone died during combat.
Hostage-taking
Taking hostages can constitute a war crime.
Hostage-taking generally involves seizing or detaining a person and using that person to compel another party to do—or refrain from doing—something as a condition for the person’s safety or release.
The Rome Statute expressly lists hostage-taking among grave breaches of the Geneva Conventions in international armed conflicts.
A normal detention of a combatant or security detainee is therefore not automatically hostage-taking. The purpose and circumstances of the detention matter.
Pillage
Pillage means unlawfully taking property during armed conflict.
It is separately recognized as a war crime. The Rome Statute includes pillage among serious violations applicable to both international and non-international armed conflicts.
The distinction between legitimate military seizure and pillage can depend on the circumstances and applicable law.
A soldier stealing personal possessions from civilians is not transformed into lawful conduct simply because it happens during a military operation.
Sexual violence
Rape and several other forms of sexual violence can constitute war crimes.
The Rome Statute includes rape, sexual slavery, enforced prostitution, forced pregnancy, enforced sterilization and other forms of sexual violence within its war-crimes provisions, subject to the applicable conflict and legal elements.
Sexual violence can also constitute a crime against humanity when committed as part of a widespread or systematic attack directed against a civilian population.
The same physical act can therefore fall into different categories of international crime depending on the surrounding circumstances.
Using children in hostilities
Recruiting or using children below the age of 15 in hostilities can constitute a war crime under the Rome Statute and applicable international law.
The legal rules concerning children in armed conflict have developed through multiple treaties and customary-law rules, and specific obligations can vary according to the instrument and conflict.
The underlying principle is that children receive special protection from the effects of armed conflict.
Prohibited weapons and methods
International law also restricts certain weapons and methods of warfare.
The Rome Statute includes, under specified circumstances, use of poison or poisoned weapons, poisonous gases and certain weapons or methods of warfare causing superfluous injury or unnecessary suffering. Some provisions apply differently depending on the type of conflict and the treaties or amendments applicable.
This is an area where legal analysis requires particular care.
Not every weapon that causes severe injury is prohibited. The legal status of a weapon can depend on treaties, customary international law, the type of weapon, how it is used and whether a particular prohibition applies to the conflict in question.
What about starving civilians?
Starvation can also be a war crime under applicable international law.
The prohibition is not limited to physically attacking civilians. International humanitarian law also protects access to essential supplies and restricts methods of warfare that deliberately deprive civilians of objects indispensable to their survival.
The Rome Statute specifically includes, under certain conditions, intentionally using starvation of civilians as a method of warfare in international armed conflicts.
Determining whether starvation constitutes a war crime can require evidence about the conduct’s purpose, the population affected, the availability of alternatives and the relevant legal framework.
International and non-international armed conflicts
The applicable rules depend partly on the classification of the conflict.
An international armed conflict generally involves states fighting one another.
A non-international armed conflict involves sustained armed violence between governmental forces and organized armed groups, or between such groups, meeting the applicable legal threshold.
The distinction matters because the treaty provisions and specific war crimes are not identical in both categories.
The Rome Statute contains separate provisions for serious violations in international armed conflicts and non-international armed conflicts.
Importantly, serious violations can constitute war crimes in both types of conflict under customary international law.
War crimes are different from crimes against humanity
The terms are sometimes used interchangeably in political reporting, but legally they describe different categories.
A war crime must have a connection to an armed conflict.
A crime against humanity, by contrast, involves specified acts committed as part of a widespread or systematic attack directed against a civilian population and does not require an armed conflict in the same way.
That means an act of torture can potentially be:
- An ordinary domestic crime
- A war crime
- A crime against humanity
The classification depends on the circumstances and the applicable legal elements.
Genocide is another distinct international crime requiring the specific intent to destroy, in whole or in part, a protected national, ethnic, racial or religious group.
Who can be held responsible?
War-crimes liability is generally individual rather than limited to states.
A person can potentially be responsible for personally committing a war crime, ordering one, or participating in it through other legally recognized forms of responsibility.
Command responsibility can also arise in appropriate circumstances. The ICRC notes that commanders and other superiors may bear criminal responsibility for crimes committed pursuant to their orders and, under applicable rules, for crimes by subordinates where they fail to take adequate measures to prevent or punish them.
That does not mean a commander is automatically responsible for every unlawful act committed by a subordinate.
The specific legal requirements must be established.
What evidence is needed?
Investigating an alleged war crime usually requires much more than proof that something terrible happened.
Evidence may include:
- Military orders and operational plans
- Targeting information
- Communications between commanders
- Satellite imagery
- Video and photographs
- Weapons fragments
- Medical and forensic evidence
- Witness testimony
- Information about the intended target
- Evidence of what commanders knew
- Records concerning detainees
- Evidence showing the broader pattern of conduct
For an alleged unlawful airstrike, for example, investigators may need to establish the intended target, whether it was a military objective, what intelligence supported the attack, which weapon was used, what civilian presence was known or foreseeable, and what precautions were taken.
That is why determining whether an attack was a war crime can take months or years.
Does intent always have to be proven?
The mental element depends on the particular offense.
Some war crimes expressly require intentional conduct—for example, intentionally directing an attack against civilians or civilian objects under the relevant provisions.
Other legal rules concern knowledge, recklessness or other specified mental elements.
The precise standard therefore cannot be reduced to “the attacker meant to kill civilians.”
A person can potentially incur criminal responsibility for a serious violation even when civilian deaths were not the intended outcome, depending on the offense and the facts.
What if both sides commit war crimes?
One side’s violations do not cancel out the other’s.
International humanitarian law applies to all parties to an armed conflict. The ICRC emphasizes that parties cannot invoke violations by an opponent as a justification for their own violations.
This is particularly important in investigations of conflicts involving multiple armed forces.
Evidence that one party committed war crimes does not establish that another party’s conduct was lawful.
Each alleged incident must be assessed against the rules applicable to it.
Who investigates and prosecutes war crimes?
National courts are generally the first line of accountability.
States have obligations under international humanitarian law to investigate and, where appropriate, prosecute serious violations. States can also exercise universal jurisdiction over certain war crimes in circumstances permitted or required by international law and domestic legislation.
International courts can also have jurisdiction in particular circumstances.
The International Criminal Court’s jurisdiction, for example, depends on the Rome Statute and its jurisdictional requirements. Its Article 8 provides an important treaty-based catalogue of war crimes, but the existence of a war crime does not automatically mean that the ICC has jurisdiction over the case.
Other international or hybrid tribunals can operate under their own mandates.
Why the distinction matters in current conflicts
When a UN investigation or another independent body describes an attack as a possible war crime, the phrase has a specific legal significance.
It does not simply mean:
“Many civilians were killed.”
Investigators are potentially alleging a serious violation of the rules governing armed conflict.
The relevant questions become much more precise: What was attacked? Was it a lawful military objective? What did the attacker know? What precautions were taken? What civilian harm was expected? What military advantage was anticipated? Which legal rule applies? And does the available evidence satisfy the required elements of the alleged offense?
Those questions explain why international investigations can reach conclusions that differ from initial political narratives.
The key test is the conduct, not the label
The phrase “war crime” carries enormous political and moral weight, but international law gives it a narrower meaning.
A serious wartime harm becomes a war crime when the conduct meets the elements of a recognized serious violation of international humanitarian law. The precise test depends on the offense, the type of armed conflict, the applicable treaties and customary law, and the evidence concerning the accused person’s conduct and mental state.
That is why the most reliable way to assess a war-crimes allegation is to move past the headline and examine the underlying evidence.
The central question is not simply whether civilians died, property was destroyed or prisoners were mistreated. It is whether the conduct violated a rule of international humanitarian law that carries individual criminal responsibility, and whether the evidence establishes the legal elements required for that particular offense. That distinction is what separates a documented tragedy or battlefield mistake from conduct that international law recognizes as a war crime.