Legal Sidebari

War Crimes: A Primer
Updated February 2, 2024
The Russian invasion of Ukraine and the Israel-Hamas conflict have given rise to numerous accusations
of war crimes. This Legal Sidebar addresses the sources and content of the law of war, also known as the
law of armed conflict or international humanitarian law (IHL) as it pertains to war crimes that occur in an
international armed conflict. IHL applies to the conduct of war; it does not address the legality of a war.
Sources of International Humanitarian Law
IHL is a combination of international treaties and customary international law. The Hague Convention of
1907 generally prescribes rules of conduct for armed forces, while the Geneva Conventions and Protocol
Additional to the Geneva Conventions of 12 August 1949, and relating to the Protection of Victims of
International Armed Conflicts 1 (Protocol 1) address the rights of protected persons, such as civilians and
prisoners of war, in an international armed conflict (i.e., a war between or among states). Non-
international armed conflicts are governed by Article 3 Common to the Geneva Conventions (Common
Article 3) and the Protocol Additional Relating to the Victims of Non-International Armed Conflicts
(Protocol 2). A non-international armed conflict under Common Article 3 is an armed conflict that takes
place “in the territory of one of the High Contracting Parties,” but the requirement has been understood to
cover armed conflicts that take place on more than one territory but involve non-state actors—an
understanding confirmed by the U.S. Supreme Court in the context of the armed conflict involving Al
Qaeda and its associated forces. Because Gaza is not part of a state, it is unclear whether the Israel-Hamas
conflict is an international (potentially involving an occupied territory) or non-international armed
conflict. In addition, not all states are parties to these and other treaties pertaining to the law of war, but
many treaty provisions are regarded as reflecting customary international law, which is binding on all
states.
Principles of International Humanitarian Law
Certain principles undergird IHL and form the basis for the content of war crimes and serve to reduce
unnecessary suffering during war. The most important principles are military necessity, humanity, and
honor. The principles of distinction and proportionality flow from the first three. The Department of
Defense’s Law of War Manual describes their interaction as follows:
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Military necessity justifies certain actions necessary to defeat the enemy as quickly and efficiently
as possible. Conversely, humanity forbids actions unnecessary to achieve that object.
Proportionality requires that even when actions may be justified by military necessity, such actions
not be unreasonable or excessive. Distinction underpins the parties’ responsibility to comport their
behavior with military necessity, humanity, and proportionality by requiring parties to a conflict to
apply certain legal categories, principally the distinction between the armed forces and the civilian
population. Lastly, honor supports the entire system and gives parties confidence in it. (Citations
omitted).
The main purposes of the law of armed conflict are:
• Protecting combatants, noncombatants, and civilians from unnecessary suffering;
• Providing certain fundamental protections for persons who fall into the hands of the
enemy, particularly prisoners of war, military wounded and sick, and civilians;
• Facilitating the restoration of peace;
• Assisting the commander in ensuring the disciplined, ethical, and effective use of military
force;
• Preserving the professionalism and humanity of combatants; and
• Preventing the degeneration of warfare into savagery or brutality.
United States Law: The War Crimes Act of 1996
The War Crimes Act (18 U.S.C. § 2441) sets forth conduct the United States punishes as war crimes.
Previously, only when U.S. nationals were involved as either perpetrator or victim would the conduct
potentially fall under these provisions. Congress amended the provision in January 2023 to provide
courts’ jurisdiction over foreign nationals who are found in the United States and suspected of having
committed war crimes anywhere. Such a prosecution requires the Attorney General or the Deputy
Attorney General to certify that “a prosecution by the United States is in the public interest and necessary
to secure substantial justice,” taking into consideration, among other things, whether it is possible to
remove the offender to another jurisdiction for prosecution as well as “potential adverse consequences for
nationals, servicemembers, or employees of the United States.” In December 2023, the United States for
the first time indicted several persons for violating the act and, according to the Attorney General, may be
considering more prosecutions. For more information, see CRS Legal Sidebar LSB 11091: The First
Prosecution Under the War Crimes Act: Overview and International Legal Context.
The act implements the United States’ obligation under treaties and international law to hold perpetrators
of war crimes accountable. A war crime under the act includes conduct “defined as a grave breach” in the
Geneva Conventions of 1949 or prohibited by certain provisions of the Annex to the Hague Convention
IV, Respecting the Laws and Customs of War on Land of 1907. The act further proscribes the willful
killing of or causing serious injuries to civilians contrary to the provisions of the Protocol on Prohibitions
or Restrictions on the Use of Mines, Booby-Traps and Other Devices. It also proscribes certain violations
defined as “a grave breach of common Article 3” of the Geneva Conventions.
The Geneva Conventions
Grave breaches as defined in the Geneva Conventions include the following acts if committed against
protected persons or property (as applicable):
• Willful killing;
• Torture or inhuman treatment, including biological experiments;

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• 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 other protected person to serve in the forces of a hostile
power;
• Willfully depriving a prisoner of war or other protected person of the rights of fair and
regular trial;
• Unlawful deportation or transfer or unlawful confinement; and
• Taking of hostages.
The Hague Convention
Violations of the Annex to the Hague Convention punishable under the War Crimes Act include
provisions forbidding combatants:
• To employ poison or poisoned weapons;
• To kill or wound treacherously individuals belonging to the hostile nation or army;
• To kill or wound an enemy who, having laid down his arms or having no longer means of
defense, has surrendered at discretion;
• To declare that no quarter will be given (“take no prisoners”);
• To employ arms, projectiles, or material calculated to cause unnecessary suffering;
• To make improper use of a flag of truce; the enemy’s national flag, military insignia, or
uniform; or the distinctive badges of the Geneva Convention;
• To destroy or seize the enemy’s property, unless such destruction or seizure be
imperatively demanded by the necessities of war;
• To declare abolished, suspended, or inadmissible in a court of law the rights and actions
of the nationals of the hostile party (a belligerent is likewise forbidden to compel the
nationals of the hostile party to take part in the operations of war directed against their
own country, even if they were in the belligerent’s service before the commencement of
the war);
• To attack or bombard, by whatever means, towns, villages, dwellings, or buildings that
are undefended;
• To attack buildings dedicated to religion, art, science, or charitable purposes; historical
monuments, hospitals, and places where the sick and wounded are collected, provided
they are not being used at the time for military purposes; and
• To pillage of a town or place, even when taken by assault.
Common Article 3
Article 3 Common to the four Geneva Conventions of 1949 provides protections during armed conflicts
not of an international nature and also protects persons during international armed conflicts who are not
entitled to protected status under any of the four conventions. Title 18, Section 2441(d), of the U.S. Code
defines grave breaches of Common Article 3 to include committing, or attempting or conspiring to
commit:
• Torture (defined in a manner similar to that used by the federal torture statute [18 U.S.C.
§§ 2340-2340A]),

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• Cruel or inhuman treatment,
• The performing of biological experiments “without a legitimate medical or dental
purpose ... endanger[ing] the body or health of such person or persons,”
• Murder of a person taking no active part in the hostilities,
• Mutilation or maiming persons taking no active part in the hostilities,
• Intentionally causing serious bodily injury,
• Rape,
• Sexual assault or abuse, and
• The taking of hostages.
The proscriptions against murder, mutilation or maiming, and causing bodily injury do not apply in cases
of collateral damage or results incident to lawful acts of warfare.
International Law
Although the War Crimes Act sets forth conduct the United States considers serious war crimes, the
United States is not party to all treaties regarding the law of armed conflict, including notably Additional
Protocol I to the Geneva Conventions (regulating international armed conflicts). The Rome Statute of the
International Criminal Court (ICC) probably provides the most complete compendium of serious war
crimes as accepted by the international community. The United States is not party to the Rome Statute but
took part in its negotiation, including regarding the inclusion of the covered war crimes.
Neither Ukraine nor Russia is party to the agreement, but Ukraine has agreed to accept the jurisdiction of
the ICC for activities that occur on its territory since 2014—and the ICC Prosecutor opened an
investigation in February 2022 to examine the situation in Ukraine, as discussed in this CRS Legal
Sidebar.
Israel is not a member of the ICC, but according to the ICC, the “Government of Palestine” acceded to the
Rome Statute in 2015. In March 2021, the ICC Prosecutor opened an investigation into possible crimes
committed within the ICC’s jurisdiction since June 13, 2014, in Gaza and the West Bank (including East
Jerusalem). The investigation is ongoing and has been extended to cover the escalation of hostilities and
violence since the attacks that took place on October 7, 2023.
In addition to grave breaches of the Geneva Conventions set forth above, the Rome Statute provides for
punishment of:
(i) Intentionally directing attacks against the civilian population as such or against individual
civilians not taking direct part in hostilities;
(ii) Intentionally directing attacks against civilian objects, that is, objects which are not military
objectives;
(iii) Intentionally directing attacks against personnel, installations, material, units or vehicles
involved in a humanitarian assistance or peacekeeping mission in accordance with the Charter of
the United Nations, as long as they are entitled to the protection given to civilians or civilian objects
under the international law of armed conflict;
(iv) Intentionally launching an attack in the knowledge that such attack will cause incidental loss of
life or injury to civilians or damage to civilian objects or widespread, long-term and severe damage
to the natural environment which would be clearly excessive in relation to the concrete and direct
overall military advantage anticipated;

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(v) Attacking or bombarding, by whatever means, towns, villages, dwellings or buildings which are
undefended and which are not military objectives;
(vi) Killing or wounding a combatant who, having laid down his arms or having no longer means
of defence, has surrendered at discretion;
(vii) Making improper use of a flag of truce, of the flag or of the military insignia and uniform of
the enemy or of the United Nations, as well as of the distinctive emblems of the Geneva
Conventions, resulting in death or serious personal injury;
(viii) The transfer, directly or indirectly, by the Occupying Power of parts of its own civilian
population into the territory it occupies, or the deportation or transfer of all or parts of the population
of the occupied territory within or outside this territory;
(ix) Intentionally directing attacks against buildings dedicated to religion, education, art, science or
charitable purposes, historic monuments, hospitals and places where the sick and wounded are
collected, provided they are not military objectives;
(x) Subjecting persons who are in the power of an adverse party to physical mutilation or to medical
or scientific experiments of any kind which are neither justified by the medical, dental or hospital
treatment of the person concerned nor carried out in his or her interest, and which cause death to or
seriously endanger the health of such person or persons;
(xi) Killing or wounding treacherously individuals belonging to the hostile nation or army;
(xii) Declaring that no quarter will be given;
(xiii) Destroying or seizing the enemy’s property unless such destruction or seizure be imperatively
demanded by the necessities of war;
(xiv) Declaring abolished, suspended or inadmissible in a court of law the rights and actions of the
nationals of the hostile party;
(xv) Compelling the nationals of the hostile party to take part in the operations of war directed
against their own country, even if they were in the belligerent’s service before the commencement
of the war;
(xvi) Pillaging a town or place, even when taken by assault;
(xvii) Employing poison or poisoned weapons;
(xviii) Employing asphyxiating, poisonous or other gases, and all analogous liquids, materials or
devices;
(xix) Employing bullets which expand or flatten easily in the human body, such as bullets with a
hard envelope which does not entirely cover the core or is pierced with incisions;
(xx) Employing weapons, projectiles and material and methods of warfare which are of a nature to
cause superfluous injury or unnecessary suffering or which are inherently indiscriminate in violation
of the international law of armed conflict, provided that such weapons, projectiles and material and
methods of warfare are the subject of a comprehensive prohibition [to be set forth in an annex];
(xxi) Committing outrages upon personal dignity, in particular humiliating and degrading treatment;
(xxii) Committing rape, sexual slavery, enforced prostitution, forced pregnancy, … enforced
sterilization, or any other form of sexual violence also constituting a grave breach of the Geneva
Conventions;
(xxiii) Utilizing the presence of a civilian or other protected person to render certain points, areas or
military forces immune from military operations;
(xxiv) Intentionally directing attacks against buildings, material, medical units and transport, and
personnel using the distinctive emblems of the Geneva Conventions in conformity with international
law;

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(xxv) Intentionally using starvation of civilians as a method of warfare by depriving them of objects
indispensable to their survival, including wilfully impeding relief supplies as provided for under the
Geneva Conventions;
(xxvi) Conscripting or enlisting children under the age of fifteen years into the national armed forces
or using them to participate actively in hostilities.
For more information about these war crimes, see the ICC list of elements of crimes. For information
about potential accountability for war crimes in international tribunals, see CRS Legal Sidebar
LSB10704, The Role of International Tribunals in the Response to the Invasion of Ukraine. For more
information about the situation in Ukraine, see CRS Report R47762, War Crimes in Ukraine.
Author Information

Jennifer K. Elsea

Legislative Attorney




Disclaimer
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to congressional committees and Members of Congress. It operates solely at the behest of and under the direction of
Congress. Information in a CRS Report should not be relied upon for purposes other than public understanding of
information that has been provided by CRS to Members of Congress in connection with CRS’s institutional role.
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