Law of armed conflict

The law of armed conflict is founded on several core principles that guide the conduct of hostilities. The principle of distinction requires parties to distinguish between combatants and civilians, and between military objectives and civilian objects, directing attacks only at the former. The principle of proportionality prohibits attacks that may cause incidental civilian harm excessive in relation to the anticipated military advantage. The principle of military necessity permits only measures that are required to achieve a legitimate military purpose, while unnecessary suffering is prohibited, banning weapons that cause superfluous injury. These principles are customary and apply to all states, even those not party to relevant treaties.

LOAC applies once an armed conflict exists, whether international (between states) or non-international (between a state and an organized armed group, or between such groups). It does not govern the legality of going to war (jus ad bellum), but rather the conduct within war (jus in bello). The determination of conflict status is factual and legal, not based on the parties' own characterizations.

The modern law of armed conflict traces its origins to the mid-19th century, notably the 1864 Geneva Convention for the Amelioration of the Condition of the Wounded in Armies in the Field, initiated by Henry Dunant after the Battle of Solferino. The 1899 and 1907 Hague Conventions codified rules on the means and methods of warfare, including the prohibition of poison weapons and the requirement to spare undefended towns. The four Geneva Conventions of 1949, now universally ratified, protect wounded and sick armed forces, shipwrecked personnel, prisoners of war, and civilians. The 1977 Additional Protocols extended protections to victims of non-international armed conflicts and updated rules on methods of warfare.

The International Committee of the Red Cross (ICRC) has played a central role in the development and promotion of LOAC, and its customary law study of 2005 identified 161 rules applicable in both international and non-international conflicts. Other instruments, such as the 1997 Ottawa Convention banning anti-personnel landmines and the 2008 Convention on Cluster Munitions, address specific weapons.¹

Enforcement of the law of armed conflict relies on a combination of national and international mechanisms. States have an obligation to investigate and prosecute war crimes committed by their nationals or on their territory, a principle known as universal jurisdiction in some cases. International tribunals, such as the International Criminal Court (ICC), the International Criminal Tribunal for the former Yugoslavia (ICTY), and the International Criminal Tribunal for Rwanda (ICTR), have prosecuted individuals for serious violations. The ICC, established by the Rome Statute in 1998, has jurisdiction over war crimes, crimes against humanity, genocide, and aggression.²

Grave breaches of the Geneva Conventions, such as willful killing, torture, and inhuman treatment, are subject to mandatory prosecution or extradition by all states parties. The principle of individual criminal responsibility holds that commanders and superiors may be liable for crimes committed by subordinates if they knew or should have known and failed to prevent them. Reparations to victims are also recognized, though often difficult to implement in practice.

Beyond the well-known rules, LOAC contains several lesser-known provisions. The 1977 Additional Protocol I prohibits the use of methods of warfare that cause widespread, long-term and severe damage to the natural environment, a rule that has gained relevance in modern conflicts. The protection of cultural property is addressed in the 1954 Hague Convention, which requires parties to refrain from using cultural sites for military purposes and to avoid making them objects of attack. The law also regulates the use of emblems, such as the red cross, red crescent, and red crystal, to identify protected persons and objects.³

Another niche area is the regulation of cyber operations. The 2021 ICRC guidelines and the 2023 report of the UN Group of Governmental Experts affirm that LOAC applies to cyber operations during armed conflict, and that the principles of distinction, proportionality, and precautions apply equally in cyberspace. Additionally, the law of neutrality, largely codified in the 1907 Hague Conventions, governs the rights and duties of neutral states during war, including restrictions on the use of neutral territory for military operations.

Jus ad bellum

The body of law governing the legality of resorting to armed force.

Jus in bello

The law governing the conduct of hostilities, synonymous with the law of armed conflict.

Grave breaches

Serious violations of the Geneva Conventions that trigger universal jurisdiction.

Universal jurisdiction

A principle allowing states to prosecute certain crimes regardless of where they were committed.