There are specific rules that govern how nations conduct armed conflicts. These are set primarily in four treaties from 1949 called the Geneva Conventions, which all countries accept and have expanded over time. They are very clear on what warring nations cannot do during a conflict, and those things that violate these principles are known as War crimes. The worst of these include: Deliberate killing that is not justified by a legitimate military objective; Wounding or killing someone who has surrendered; Attacking civilians who are not participating in the conflict; and starving people to death as a weapon of war.
In the case of the ICC, the prosecution is based on a test of command responsibility: “A person commits a war crime when, in a position of authority as part of an armed group, he or she participates in planning, preparing, initiating, or waging a war of aggression or a war contrary to international humanitarian law” (ICC Statute, Elements of Crimes, SS 8). Several big and powerful countries have rejected the court’s jurisdiction, making it difficult for its authorities to arrest suspects. Even when arrest warrants are issued, some national leaders have traveled abroad after being indicted and have not been arrested.
For most of us, the word “War crime” has negative connotations. That is understandable. It is a loaded term that sends out contradictory emotive signals: It carries the sense of extreme, barbarous behavior, but also conveys a judgment that the act is morally wrong. It can cause the public to lose faith in the war effort, as did happen when a scathing report on the U.S. Army massacre of Vietnamese persons at My Lai was published in 1968.