Module 2: International Criminal Law & the Use of Force

UN Charter Article 2(4) broadly prohibits the threat or use of force against any state’s territorial integrity or political independence — the foundational modern rule governing relations between states, subject to narrow, recognized exceptions.

Example. State Alpha threatens to invade State Beta’s territory over an unrelated trade dispute, with no armed attack from Beta and no Security Council authorization — squarely prohibited by Article 2(4), with no recognized exception applying.

Armed Activities on the Territory of the Congo (Democratic Republic of the Congo v. Uganda), 2005 I.C.J. 168, is a real, modern illustration of Article 2(4) actually being enforced against a state’s claimed justifications. Ugandan forces had entered and occupied territory in the DRC during the late 1990s and early 2000s, and Uganda argued its presence was justified by consent from the DRC’s own government and by self-defense against rebel groups operating from Congolese territory. The ICJ rejected both justifications on the actual facts, holding Uganda’s military occupation and support for rebel groups within the DRC violated Article 2(4) and the broader customary prohibition on the use of force, and separately violated international humanitarian law through the conduct of Ugandan troops during the occupation. The Court ordered Uganda to pay reparations. Armed Activities is a genuinely useful modern reminder that Article 2(4) isn’t simply a Cold War-era relic — states in the 2000s and beyond have continued to test its boundaries, and continued to lose before the ICJ when their justifications didn’t hold up.

Two recognized lawful exceptions to Article 2(4): self-defense under Article 51 (requiring an actual armed attack, and a necessary and proportional response), and Security Council authorization under Chapter VII (the Council determines a threat to the peace and authorizes measures, potentially including force).

Example. State Beta launches concrete, ongoing cross-border shelling attacks against State Alpha — Alpha’s proportional military response is likely lawful self-defense under Article 51. Now compare: instead of acting alone, the Security Council formally determines the situation threatens international peace and authorizes “all necessary means” — any resulting force by authorized states is lawful under Chapter VII, an entirely separate and independent basis from Article 51.

Nicaragua v. United States, 1986 I.C.J. 14 — the same real case whose enforcement failure this course’s ICJ module already covers — is, on its actual merits, the foundational modern case defining Article 51’s “armed attack” threshold. The United States argued its support for the Contra rebels fighting Nicaragua’s government was collective self-defense on behalf of Nicaragua’s neighbors, responding to Nicaraguan support for rebels in their own territory. The ICJ drew a real, substantive line: not every frontier incident or lower-level use of force rises to the “armed attack” scale and effects Article 51 requires before self-defense becomes available at all — a state can violate the general Article 2(4) prohibition through some use of force without that force necessarily amounting to the kind of “armed attack” that would justify a forceful, self-defense response from another state. Nicaragua is the real doctrinal source of the distinction this section relies on between the general prohibition’s broad reach and the narrower, higher-threshold trigger for a lawful self-defense response.

Once a conflict begins, jus in bello (distinct from jus ad bellum, which governs whether resorting to force was lawful) governs how it must be fought: distinction (attack only combatants/military objectives), proportionality (don’t cause civilian harm excessive relative to the military advantage), and military necessity (force limited to what a legitimate military purpose actually requires).

Example. Forces deliberately target a hospital treating only civilians, with no military objective, purely to demoralize the population — a clear distinction violation, regardless of whether the broader conflict itself is lawful. Now compare: forces strike a legitimate military target, anticipating limited, unavoidable civilian harm relative to a real, concrete military advantage — likely satisfies proportionality, even though some civilian harm still occurs.

Prosecutor v. Stanislav Galić, decided by the International Criminal Tribunal for the former Yugoslavia in 2003, applied the distinction principle to real, documented wartime conduct. Galić commanded Bosnian Serb forces during the siege of Sarajevo, and the prosecution presented extensive evidence of a sustained sniping and shelling campaign deliberately targeting civilians going about ordinary daily activities — standing in bread lines, crossing streets, attending funerals — with no claimed military objective connected to those individual acts. The Tribunal convicted Galić, holding that a campaign of violence whose primary purpose is spreading terror among the civilian population is itself a distinct, serious violation of international humanitarian law, independent of any individual proportionality calculation for a specific strike. Galić was the first individual convicted by an international tribunal specifically for a terror campaign against civilians, and remains a genuinely concrete illustration of how distinction operates not just strike-by-strike, but as a real constraint on an entire military campaign’s underlying strategy.

Genocide requires an enumerated act against a protected group (national, ethnical, racial, or religious), with the demanding specific intent (dolus specialis) to destroy the group, in whole or in part, as such — the element that most distinguishes genocide from other grave crimes.

Example. Forces specifically target and kill members of an ethnic minority group, clearly expressing intent to eliminate the group entirely from the region — likely genocide, given the clear specific intent. Now compare: forces commit widespread killing during a conflict without any evidence of intent to destroy a protected group as such — likely a war crime or crime against humanity instead, but not genocide, absent that demanding specific-intent element.

Prosecutor v. Jean-Paul Akayesu, decided by the International Criminal Tribunal for Rwanda in 1998, was the very first genocide conviction by any international tribunal, on real, documented facts from the 1994 Rwandan genocide. Akayesu was the bourgmestre (local mayor) of Taba commune, where Tutsi civilians were systematically killed and subjected to sexual violence with clear, express intent to destroy the Tutsi population as a group. The Tribunal’s judgment did more than convict Akayesu — it also established, for the first time in international law, that rape and sexual violence could themselves constitute genocide when committed with the specific intent to destroy a protected group, since such acts can inflict the kind of serious bodily and mental harm the Genocide Convention’s enumerated acts already cover. Akayesu is the real foundational case behind the modern, more expansive understanding of what “an enumerated act” can actually include, and remains the direct ancestor of every genocide prosecution since.

Crimes against humanity require an underlying act (murder, torture, deportation, persecution) committed as part of a widespread or systematic attack against a civilian population, with the perpetrator’s knowledge of that broader attack — no specific intent to destroy a protected group is required, a meaningfully lower bar than genocide.

Example. A government carries out an organized, widespread campaign of arbitrary detention and torture against political opponents, with no evidence of intent to destroy any protected group — likely crimes against humanity, since the widespread/systematic attack and knowledge elements are satisfied, even without genocide’s specific-intent requirement (and even though political opponents aren’t a protected group under the traditional genocide categories).

Prosecutor v. Duško Tadić was the very first case tried before the International Criminal Tribunal for the former Yugoslavia, with its trial judgment issued in 1997 on real facts from the Bosnian War. Tadić, a local Bosnian Serb politician and camp guard, was shown to have personally participated in the mistreatment and killing of Bosnian Muslim and Croat detainees at the Omarska and Keraterm camps, as part of a documented, systematic campaign of ethnic cleansing across the surrounding region. The Tribunal’s judgment helped establish, in real, modern practice, that crimes against humanity don’t require any connection to an international armed conflict specifically, and that the “widespread or systematic attack” element could be satisfied by a documented regional campaign rather than requiring proof of some single, centrally coordinated national plan. Tadić — ICTY’s first-ever completed trial — is the real, foundational case behind the modern crimes-against-humanity framework this section relies on.

War crimes are serious violations of the laws and customs of armed conflict, including “grave breaches” of the Geneva Conventions — requiring a nexus to an actual armed conflict, unlike crimes against humanity, which don’t require one. Command responsibility can hold superiors liable for subordinates’ crimes they knew or should have known about and failed to prevent or punish; superior orders generally isn’t a complete defense.

Example. A general orders subordinates to execute captured, unarmed civilians during an ongoing armed conflict; the soldiers comply, aware the order is manifestly unlawful — a war crime for the soldiers (superior orders isn’t a complete defense) and, separately, direct and command-responsibility liability for the general who gave the order.

Prosecutor v. Zejnil Delalić et al. (the “Čelebići Case”), decided by the ICTY’s Trial Chamber in 1998, is the real modern case that revived and refined command responsibility doctrine for contemporary international criminal law. The case concerned mistreatment of detainees at the Čelebići prison camp during the Bosnian War, and one defendant, Zdravko Mucić, was the camp’s commander at the time of the abuses even though he hadn’t personally committed them. The Tribunal convicted Mucić under command responsibility, holding a superior can be criminally liable for subordinates’ crimes where the superior had effective control over the subordinates, knew or had reason to know crimes were being or had been committed, and failed to take necessary and reasonable measures to prevent or punish them. Čelebići is the direct modern source of the three-element command responsibility framework — effective control, actual or constructive knowledge, and failure to act — this section relies on.

The crime of aggression is a leadership crime — the planning, preparation, initiation, or execution of a manifest UN Charter violation, by someone in a position to effectively control or direct a state’s political or military action, distinct from ordinary war crimes or crimes against humanity liability that can reach lower-level actors too.

Example. A head of state orders a manifestly unlawful invasion of a neighboring country with no self-defense or Security Council basis at all — the crime of aggression targets that head of state specifically, as someone with effective control over the decision, distinct from (though potentially alongside) any war crimes or crimes against humanity charges arising from how the resulting conflict was actually conducted.

The crime of aggression’s real lineage traces directly back to the Nuremberg Trials. The 1945 London Charter establishing the Nuremberg Tribunal defined “Crimes against Peace” — planning, preparation, initiation, or waging of a war of aggression — as one of its core charges, and the Tribunal’s own judgment famously called this “the supreme international crime, differing only from other war crimes in that it contains within itself the accumulated evil of the whole.” That leadership-focused framing carried directly into the modern Rome Statute crime of aggression, though the ICC’s own version of the crime has a real, distinct history of its own: the Rome Statute originally listed aggression as a crime in 1998 without yet defining it or giving the Court actual jurisdiction over it, and it took the 2010 Kampala Review Conference to adopt the crime’s actual definition and jurisdictional conditions — which didn’t themselves take effect until 2018, twenty years after the Rome Statute’s original adoption. That real, two-decade gap between naming the crime and the Court actually being able to prosecute it reflects just how genuinely contested defining a state-leadership crime of this kind has remained since Nuremberg.