The IHL defines three fundamental principles governing the conduct of hostilities, meaning the conflict between the parties to the conflict: distinction, proportionality, and precautions. These principles are of customary nature and must be respected at all times by all parties – states, non-state armed groups, and civilian persons directly participating in hostilities – in all armed conflicts, whether international or non-international. Certain categories of persons and goods, such as units, means of transport, and medical personnel, goods essential for the survival of the civilian population, as well as installations containing dangerous forces, benefit from stricter additional protective measures (see below the question of protecting civilian infrastructures).
The principles and rules governing the conduct of hostilities apply in all cases where combat takes place within the context of an armed conflict, whether on land (ground operations), in the air (aerial warfare), at sea (naval warfare), in the cyber realm (cyber operations), and in outer space.
The principles and rules of IHL governing the conduct of hostilities aim to protect the civilian population against the effects of hostilities, by ensuring a balance between military necessity and humanitarian requirements, through prohibitions and restrictions concerning weapons, means, and methods of warfare that parties to the conflict may resort to.
The principle of distinction requires parties to the conflict to always distinguish between civilians and combatants, as well as between military objectives and civilian property, such as dwellings, civilian infrastructure, and the environment. Parties may only direct their attacks against combatants, never civilians, and may only target military objectives and never civilian property. Attacks without distinction, meaning attacks not directed at specific military objectives in accordance with the rules, that cannot be targeted in this manner, or whose effects cannot be contained as required by international humanitarian law, are also prohibited. Threats of violence aimed at spreading terror among the civilian population, as well as the use of famine as a method of war against the civilian population, are also prohibited.
Attacks targeting combatants or other military objectives must respect the principle of proportionality. This principle prohibits launching an attack that may be expected to incidentally cause loss of civilian life, injury to civilians, or damage to civilian property, which would be excessive in relation to the concrete and direct military advantage expected. In other words, any attack on a military objective must be preceded by an evaluation leading to the conclusion that civilian losses and damages are not disproportionate to the expected military advantage.
The precautionary principle requires all parties to a conflict to constantly ensure the protection of the civilian population and civilian property against the effects of military operations. Given the significant risk of harm to civilians in case of attack, IHL imposes detailed obligations on those who plan, decide, or carry out attacks. In particular, all practically possible precautions should be taken to: – Verify that the targets are military objectives; – Avoid and, in any case, minimize civilian casualties, injuries to civilians, and damage to civilian property that could be incidentally caused; – Evaluate if the attack is likely to violate the principle of proportionality; – Cancel or suspend an attack if it appears that it would violate the principle of distinction or the rule of proportionality; – Provide timely warnings by effective means in case of attacks that may affect the civilian population.
IHL also requires parties to the conflict to protect the civilian population and civilian property under their authority against the effects of attacks. In cities, military and civilian personnel and property are often closely intertwined. For parties involved in hostilities taking place in urban or other populated areas, this mixture poses significant challenges, both militarily and to avoid harm to civilians. As warfare in urban areas poses specific dangers to civilians, protection provided by the principles and rules of IHL is crucial.
