Law and morality in war

Three bodies of international law are relevant to how wars must be waged. First, general international law prohibits states from starting wars in most circumstances. This general prohibition on the use of force is enshrined in the Charter of the United Nations.

International law is not enforced in the way domestic law is enforced. The blueprint for legal enforcement that most of us have in mind is that if you threaten someone with violence or use violence against somebody, the police would come, a court would then decide whether you broke the law, potentially issue an arrest warrant and the police would execute this arrest warrant and put you in jail. This is not how it works in the international system. We have courts that can adjudicate whether a state broke the law, but these courts do not have jurisdiction over every legal question that arises in international relations. For instance, the International Court of Justice, when it has jurisdiction, can determine that a state violated international law. The Court can order that state to cease the illegal conduct; it can impose a demand of reparations, but there is no international police force that will execute the Court’s orders.

International law is enforced in a “horizontal” system, which means states are supposed to enforce the law vis-à-vis each other, rather than a “vertical” system in which a sovereign with a police force enforces the law vis-à-vis the subjects. Generally, when a state is found to have violated international law, other states are called upon to impose sanctions, cease trade and protest diplomatically. Moreover, there is a rule in international law that states are not allowed to aid or assist another state in violating international law. Of course, that system of “horizontal” enforcement is often disrupted by politics, because states may not have an interest in “enforcing” a particular international law. There is also some vertical enforcement in international law: The UN Security Council is in charge of enforcing the international law that prohibits the use of force. The Security Council can mandate the defensive use of force in response to an aggression.

One of the greatest achievements of international law was the UN Charter in 1945, articulating a blanket prohibition on the use of force by states in international relations. Historically, war between states was considered a tool of sovereign statecraft. Following a process of gradual delegitimization of war, which culminated in the UN Charter, Article two now demands that states resolve their conflicts peacefully and not use force in their international relations. There is a customary prohibition that echoes the treaty. There are some exceptions to the prohibition on the use of force. Two are particularly important. First, the Security Council can mandate the use of force in response to an aggression. The Security Council can diagnose that there is a threat to the peace, breach of the peace or act of aggression, and then mandate a response that includes the use of force. States that take up that mandate would then be going to war in compliance with international law rather than in contravention of it.

In 1990, Iraq invaded its neighboring country Kuwait, and in response, the Security Council authorized that states cooperating with Kuwait could assist in repelling the armed attack by Iraq using “all necessary means”. That is one example of a mandate by the Security Council for the use of force.

When it comes to how states or armed groups must behave on the battlefield, we look to a series of treaties called the Geneva Conventions. They contain many provisions that are also customary law. The Geneva Conventions and Protocols are the most important treaties regulating how wars must unfold, how parties to a war must use force on the battlefield and how they must treat detainees. They also regulate humanitarian operations and occupation. For the conduct of hostilities – how belligerent parties at war use kinetic force against each other – three principles are particularly relevant, called the principles of necessity, distinction and proportionality.

Even if an attack is targeted appropriately, the attacker may be able to foresee that the attack causes some damage to civilian infrastructure or harm to civilians as a side effect.

There are divergences between what international law prescribes and what a moral approach to permissible killing would imply. International humanitarian law does not prohibit attacks against combatants, but a combatant can simply be someone conscripted into the armed forces of their state and compelled to fight for an unjust cause. Alternatively, a combatant might be fighting for a just cause.

In the war between Russia and Ukraine, Russia is conducting an illegal and immoral aggression while Ukrainian soldiers are acting in self-defense. From a moral point of view, soldiers who act in self-defense are not liable to harming, as they have done nothing wrong. However, international humanitarian law addresses Russian and Ukrainian soldiers with the exact same rules. This is a significant divergence between morality and law. The divergence exists for a moral reason: if law established one set of permissive rules for the just defender and another restrictive set for the unjust aggressor, the restrictive rules for aggressors would never be applied, and the unjust aggressor would simply use the permissive rules for defenders. For law to be complied with, it must be the same for both sides, even if this allows unjust combatants to kill just ones.

International Humanitarian Law is very old. It evolved specifically to regulate conduct in war. In the Geneva Conventions we have a modern articulation of the old laws of war. Still, they are not particularly morally ambitious because they must elicit compliance in the reality of war. The laws of war do not prohibit conduct that may be morally abhorrent; they do not protect soldiers fighting for a just cause, and they do not prohibit killing civilians foreseeably. Our intuitions about permissible violence are better reflected in human rights law, which regulates relations between states and citizens in peacetime. The traditional understanding was that human rights law applies in peacetime and humanitarian law applies during war. That understanding has been criticized with the view gaining traction that human rights obligations continue to apply in war, at least where discharging them is possible. The dominant understanding now is that humanitarian law primarily governs the conduct of hostilities, but where a state has effective control over individuals during war – for example, when detaining them or as an occupying power – the state must also meet its human rights obligations.

The fact that international law is not reliably enforced is not the primary reason for non-compliance. States comply with international law for many reasons, and fear of sanctions is only one of them. Law bestows legitimacy; it helps coordination; and it carries moral authority. The most important way to improve compliance with international law is for states to consistently demand compliance, not only from adversaries but also from allies. Enforcement is most effective vis-à-vis allies, over whom states have the most influence. The current crisis of compliance in International Humanitarian Law is not due to any particular weakness of that body of law but to a lack of political courage. States must be willing to impose consequences on allies who violate the law, even if that is politically costly.

There are several misconceptions about international law in war. The most important is that highly legalized war is somehow not a moral catastrophe. It is.