How Does the Military Justice System Intersect with International Humanitarian Law and the Law of Armed Conflict?

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When a U.S. service member is accused of killing a civilian, abusing a detainee, or executing a prisoner, the charge sheet does not say “war crime.” It says murder, or assault, or maltreatment. That gap between how the conduct is described in international law and how it is actually prosecuted is the central feature of how the American military justice system enforces the law of armed conflict. The United States binds its forces to the Geneva and Hague rules, but it punishes violations almost entirely through the ordinary punitive articles of the Uniform Code of Military Justice, tried in the same courts-martial that handle every other offense.

The Law of Armed Conflict Binds U.S. Forces, but the UCMJ Is the Enforcement Tool

The law of armed conflict, also called international humanitarian law, comes from the four Geneva Conventions of 1949, the Hague Conventions of 1907, and a body of customary international law. The United States is a party to the Geneva Conventions and treats much of the Hague and customary rules as binding on its armed forces. The Department of Defense Law of War Manual, issued in 2015 and updated several times since, is the doctrinal statement of how the U.S. military reads these obligations.

What that doctrine does not do is create a freestanding criminal offense. There is no “Article for war crimes” in the UCMJ the way there is an article for desertion or larceny. Instead, when conduct in combat violates the law of war, prosecutors reach for the existing punitive articles that already prohibit the underlying act. A deliberate killing of a noncombatant is charged as murder under Article 118 (10 U.S.C. 918). Beating a detainee is assault under Article 128. Mistreating a prisoner under one’s control can be maltreatment under Article 93. Conduct that violates the law of war but does not fit a more specific article can be charged under Article 134, the general article, including by assimilating a federal statute. The law-of-war violation supplies the gravity and the context; the punitive article supplies the elements the government must prove beyond a reasonable doubt.

This routing has a practical consequence that distinguishes the U.S. approach from an international tribunal. An international court asks whether the accused committed a “war crime” as that term is defined in treaty law. A court-martial asks whether the accused committed murder, or assault, or dereliction, with all the ordinary elements, defenses, and sentencing rules that attach to those domestic offenses. The international-law label informs the charge but is not itself the charge.

Command Responsibility Without a Command-Responsibility Article

International humanitarian law recognizes command responsibility: a commander can be criminally liable for crimes committed by subordinates that the commander knew, or should have known, were being committed and failed to prevent or punish. The customary formulation, reflected in the post-Second World War proceeding against General Tomoyuki Yamashita, reaches a commander who should have known of widespread atrocities by troops under effective control.

Here the gap between doctrine and prosecution is at its widest, because the UCMJ contains no command-responsibility offense. A military prosecutor cannot simply charge a commander with “command responsibility.” The conduct has to be fitted into an existing article. The most common vehicle is dereliction of duty under Article 92 (10 U.S.C. 892), on the theory that a commander who failed to control subordinates or failed to act on knowledge of their crimes was derelict in a known duty. Where the commander actively participated, encouraged, or ordered the misconduct, the government can charge that commander as a principal under Article 77 (10 U.S.C. 877), which makes one who aids, abets, counsels, or commands an offense liable as if they committed it directly, or pursue a conspiracy theory under Article 81.

The knowledge standard the U.S. has applied in practice is also narrower than the customary international one. In the 1971 court-martial arising from the My Lai killings, Captain Ernest Medina was acquitted, and the case is read as applying an actual-knowledge standard: liability turned on whether the commander in fact knew his troops were committing the crimes and wrongfully failed to act, rather than the broader “should have known” imputed-knowledge test associated with Yamashita. A service member analyzing potential command liability under the American system therefore confronts two layers at once: the international rule that uses a should-have-known standard, and the domestic charging reality that funnels everything through dereliction, principal, or conspiracy theories, often with a stricter knowledge showing.

The “Following Orders” Limit and the Reasonable Soldier

The mirror image of command liability is the subordinate’s defense of obedience to orders. Rule for Courts-Martial 916(d) makes lawful orders a complete defense and presumes orders to be lawful, but it withdraws that defense when “the accused knew the orders to be unlawful or a person of ordinary sense and understanding would have known the orders to be unlawful.” The test is objective: it does not ask only what this particular accused believed, but what a reasonable service member in the same circumstances would have recognized.

The governing precedent is United States v. Calley, the 1973 appellate decision affirming the My Lai murder conviction, which held that an order to kill unresisting civilians under one’s control is one that a person of ordinary sense and understanding would know to be unlawful, so obedience is no defense. The practical effect is a sliding scale. Ambiguous tactical orders in a chaotic firefight enjoy the presumption of lawfulness and a strong obedience defense; a manifestly criminal order, such as executing detainees or unarmed civilians, falls outside the defense entirely, and the soldier who carries it out remains liable for the underlying offense.

The Geneva Conventions, Detainee Cases, and the Battlefield Evidence Problem

The Geneva Conventions set the substantive standards that combat conduct is measured against: protection of the wounded and sick, humane treatment of prisoners of war, and protection of civilians. Those standards are woven into U.S. rules of engagement and training, so a violation often surfaces first as an ROE breach. An ROE violation is not automatically a crime; it becomes a court-martial offense only when the conduct also satisfies the elements of a punitive article, and the government must show the rule imposed a binding obligation that the accused actually violated. Detainee-abuse prosecutions, including those arising from the Abu Ghraib scandal, illustrate the pattern: the cases were tried as assault, maltreatment, dereliction, and conspiracy charges, and they squarely raised the obedience-to-orders defense and the criminal exposure of personnel at different rungs of the chain of command.

Combat prosecutions also carry evidentiary burdens that ordinary cases do not. Physical evidence may be destroyed, contaminated, or beyond reach; witnesses may be deployed, killed, or hostile foreign nationals; and the factfinder must weigh conduct against the fear and split-second judgment inherent in armed conflict. These realities do not change the elements of the offense, but they shape what the government can prove.

Two Other Doors: Federal War-Crimes Prosecution and International Courts

The court-martial is not the only forum. The War Crimes Act, 18 U.S.C. 2441, is a federal civilian statute that makes it a crime for a U.S. national or member of the armed forces to commit a war crime, defined to include grave breaches of the 1949 Geneva Conventions, specified Hague Convention IV prohibitions, and grave breaches of common Article 3. It carries penalties up to life imprisonment, or death if the victim dies, and a prosecution may be brought even when the offense occurred entirely abroad. Critically, no prosecution may proceed without the written certification of the Attorney General, the Deputy Attorney General, or an Assistant Attorney General that the prosecution is in the public interest, a requirement that cannot be delegated. In practice the act has been used rarely; for service members on active duty, the court-martial remains the routine forum, with the federal statute available as a distinct civilian route.

Internationally, the United States has signed but never ratified the Rome Statute and is not a party to the International Criminal Court. Its stated position rests on complementarity: the ICC is meant to act only where a national system is unwilling or genuinely unable to investigate and prosecute, and the U.S. maintains that its own military justice system is capable of doing so. That is precisely why the question of how courts-martial actually charge and try law-of-war violations matters beyond the individual case. The credibility of the domestic system is the argument against external jurisdiction.

A separate and often misunderstood provision is Article 18 of the UCMJ (10 U.S.C. 818), which gives general courts-martial jurisdiction “to try any person who by the law of war is subject to trial by a military tribunal.” That clause is about the reach of military tribunals over enemy belligerents and others triable under the law of war, not the mechanism for prosecuting U.S. service members, who are tried under the ordinary punitive articles by virtue of their status.

Why the Charging Mechanics Are the Whole Story

The decisive fact about how the United States enforces the law of armed conflict against its own forces is that the international rules are not self-executing in a court-martial. They define what is wrong; the UCMJ defines what is charged and what must be proven. A killing becomes a murder case, an abused prisoner becomes a maltreatment case, a negligent commander becomes a dereliction case, and a freestanding “war crime” or “command responsibility” charge is simply unavailable. The Geneva and Hague obligations are real and binding, but they are enforced through domestic criminal law, by domestic courts-martial, under domestic elements and defenses, which is both the system’s answer to international accountability and the reason its charging mechanics deserve close attention.

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Disclaimer

This article is for general informational purposes only and is not legal advice. It describes military law and procedure of public record, does not address any individual case, and does not create an attorney-client relationship.

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