The term “war crimes” evokes a litany of horrific images—concentration camps, ethnic cleansing, execution of prisoners, rape, and bombardment of cities. These images correspond in many ways to the legal definitions of the term, but international law draws lines that do not in all ways match our sense of the most awful behavior.

War crimes are those violations of the laws of war—or international humanitarian law (IHL)—that incur individual criminal responsibility. While limitations on the conduct of armed conflict date back at least to the Chinese warrior Sun Tzu (sixth century b.c.e.), the ancient Greeks were among the first to regard such prohibitions as law. The notion of war crimes per se appeared more fully in the Hindu code of Manu (circa 200 b.c.e.), and eventually made its way into Roman and European law. The first true trial for war crimes is generally considered to be that of Peter von Hagenbach, who was tried in 1474 in Austria and sentenced to death for wartime atrocities.

By World War I, States had accepted that certain violations of the laws of war—much of which had been codified in the Hague Conventions of 1899 and 1907—were crimes. The 1945 Charter of the International Military Tribunal at Nuremberg defined war crimes as “violations of the laws or customs of war,” including murder, ill-treatment, or deportation of civilians in occupied territory; murder or ill-treatment of prisoners of war; killing of hostages; plunder of public or private property; wanton destruction of municipalities; and devastation not militarily necessary.

The 1949 Geneva Conventions, which codified IHL after World War II, also marked the first inclusion in a humanitarian law treaty of a set of war crimes—the grave breaches of the conventions. Each of the four Geneva Conventions (on wounded and sick on land, wounded and sick at sea, prisoners of war, and civilians) contains its own list of grave breaches. The list in its totality is: willful killing; torture or inhuman treatment (including medical experiments); willfully causing great suffering or serious injury to body or health; extensive destruction and appropriation of property not justified by military necessity and carried out unlawfully and wantonly; compelling a prisoner of war or civilian to serve in the forces of the hostile power; willfully depriving a prisoner of war or protected civilian of the rights of a fair and regular trial; unlawful deportation or transfer of a protected civilian; unlawful confinement of a protected civilian; and taking of hostages. Additional Protocol I of 1977 expanded the protections of the Geneva Conventions for international conflicts to include as grave breaches: certain medical experimentation; making civilians and nondefended localities the object or inevitable victims of attack; the perfidious use of the Red Cross or Red Crescent emblem; transfer of an occupying power of parts of its population to occupied territory; unjustifiable delays in repatriation of POWs; apartheid; attack on historic monuments; and depriving protected persons of a fair trial. Under the Geneva Conventions and Additional Protocol I, States must prosecute persons accused of grave breaches or hand them over to a State willing to do so.

The grave breaches provisions only apply in international armed conflicts; and they only apply to acts against so-called protected persons or during battlefield activities. Protected persons are, in general, wounded and sick combatants on land and sea, POWs, and civilians who find themselves in the hands of a state of which they are not nationals.

Most violations of the Geneva Conventions and Additional Protocols are not grave breaches. Of those not listed as grave breaches, many are still considered war crimes, although in those cases States do not have the same obligation to extradite or prosecute as they do for grave breaches. Other nongrave breaches are not war crimes, but simply illegal acts for which only the violating State is responsible under international law. To give one simple example, if the commander of a POW camp failed to keep a record of all disciplinary punishments (a violation of Article 96 of the Third Geneva Convention), he would likely not be committing a war crime—although some may disagree. Distinguishing among nongrave breaches to determine which are crimes is not an exact science, though it would seem that the more serious nongrave breaches do incur individual responsibility. (The U.S. military maintains that all violations of the laws of war, including those of the Geneva Conventions, are war crimes.)

Wartime atrocities not prohibited under the Geneva Conventions or Additional Protocol I may nonetheless be war crimes under the customary law rubric of “violations of the laws and customs of war” (the same phrase as in the Nuremberg Charter). For interstate conflicts, states agree that such war crimes include certain violations of the 1907 Hague Convention and Regulations, such as use of poisonous weapons, wanton destruction of cities not justified by military necessity, attacks on undefended localities, attacks on religious and cultural institutions, and plunder of public and private property. The Statute of the International Criminal Court (ICC) lists as war crimes for international conflicts not only the grave breaches of the Geneva Conventions, but some twenty-six serious violations of the laws and customs of war, most of which have been considered by States as crimes since at least World War II.

As for civil wars, unfortunately, international law today has fewer rules regulating the conduct of internal conflicts, which many States consider part of their domestic jurisdiction and, consequently, there is a shorter list of war crimes. Additional Protocol II of 1977, which contains basic rules for the conduct of internal conflicts, has no criminal liability provisions, and the reach of customary law war crimes is not as clear with respect to such wars as it is for international wars. The Statute of the International Criminal Tribunal for the Former Yugoslavia includes “serious violations of Common Article 3 of the Geneva Conventions” (the one article of the Geneva Conventions that addresses civil wars), as well as other rules to protect victims of armed conflict and basic rules on methods of warfare. The tribunal defined a serious violation as one that has grave consequences for its victims and breaks a rule protecting important values. This would presumably include violence to life or health (murder, ill-treatment, torture, mutilation, corporal punishment, rape, enforced prostitution, indecent assault), summary executions, hostage taking, collective punishment, and pillage. This list, while shorter than the list of grave breaches or other interstate war crimes, nonetheless would cover some of the most horrific acts during recent conflicts. The Statute of the International Criminal Tribunal for Rwanda includes as war crimes serious violations of Common Article 3 as well as serious violations of Additional Protocol II. The Statute of the ICC lists as war crimes for internal conflicts four serious violations of Common Article 3 (violence to life and person, outrages upon personal dignity, hostage taking, and summary executions), as well as twelve serious violations of the laws and customs of war (e.g., attacks on civilians, pillage, rape, or mutilation).

Though perhaps an obvious point, it should be noted that the laws of war only cover atrocities during armed conflict. They exclude many of the worst abuses of this century, such as Stalin’s purges and destruction of the Kulaks, most of the Khmer Rouge’s terror, and Mao’s forced collectivizations. While these atrocities are international crimes—crimes against humanity, or, in some cases, genocide—they are not war crimes.

The definitional nexus of war crimes to armed conflict means that the atrocities against civilians committed by actors identified as terrorists do not always fit neatly within the existing categories of war crimes. As a general matter, it can be argued that the war paradigm and war crimes moniker simply should not apply to most of their actions, as they are engaged not in a war (interstate or civil), where international law accepts much belligerent activity as lawful, but rather in a criminal enterprise in which all acts are illegal. In this sense neither the Geneva Conventions nor customary law regarding war crimes captures the nature of their crimes. Insofar as terrorist activities by non-State actors are committed as part of a more paradigmatic interstate or civil war, e.g., an insurgent group working for one side blows up a civilian bus, these could well constitute grave breaches of the Geneva Conventions or other violations of the laws and customs of war, including those applying to civil conflicts. The United States government seems to hold that some terrorist acts, even those not associated with existing interstate or civil wars, are indeed “violations of the laws and customs of war.” It is currently trying some suspected terrorists before military commissions at Guantanamo Bay for various offenses that it concludes are, in the words of an instruction to the commissions, “violations of the law of armed conflict or offenses that, consistent with that body of law, are triable by military commissions.” The foregoing considerations make any determination whether the attacks on New York, Bali, Madrid, or elsewhere by al-Qaeda are war crimes a matter of debate. The far simpler legal characterization is to identify them as crimes against humanity, which lacks any required nexus to armed conflict.

Finally, the creation of a body of law criminalizing certain violations of the laws of war does not mean that war criminals will actually be prosecuted. This remains a matter for States and, increasingly, the United Nations and other international organizations. The Geneva Conventions require all parties to search for and either extradite or try all persons suspected of having committed grave breaches. And international law gives all States the legal right to prosecute war criminals under the theory of universal jurisdiction. While States have at times prosecuted war criminals (e.g., the U.S. trial of the My Lai offenders), the more pervasive pattern, despite the obligations of the Geneva Conventions, is either mere administrative punishment or impunity. The ad hoc tribunals for Yugoslavia and Rwanda have jurisdiction over both grave breaches of the Geneva Conventions and other crimes committed in these particular conflicts, and the ICC, as noted, has jurisdiction over most war crimes.

(See international vs. internal armed conflict)