War Crimes: A Primer
March 15, 2022
The Russian invasion of Ukraine has 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 the war itself. 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, by
Nina M. Hart and Stephen P. Mulligan.
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. Not all states are parties to these and other treaties
pertaining to the law of war, but many 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:
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).
