Law of war

• 1. Rules For The Unruly

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  Creating laws for something as inherently lawless as war seems like a lesson in absurdity. That objection has followed the law of war for as long as it has existed. Yet around 1750 B.C., the Babylonian king Hammurabi already wrote a code of conduct for wartime, justifying it in plain words: I prescribe these laws so that the strong do not oppress the weak. The law of war is the branch of international law that governs two distinct questions. One is when a nation may begin a war, called jus ad bellum. The other is how hostilities may be conducted once war is underway, called jus in bello. From those two questions flow definitions of sovereignty, nationhood, occupation, and the treatment of prisoners. How did rules forbidding the killing of children and the cutting of fruit trees travel from ancient scripture into binding treaties? Why did one historian call a fifty-year window the law's epoch of highest repute? And how can rules written by mutual consent bind even the nations that never signed them?

• 2. Voices Before Treaties

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  The Book of Deuteronomy, in chapter 20, verses 19 to 20, limits the environmental damage of a siege. It permits cutting down non-fruitful trees for the siege works while ordering that fruitful trees be preserved as a food source. A later passage, verses 10 to 14 of chapter 21, addresses female captives forced to marry their captors. If no longer desired, they must be let go wherever they wish, never treated as slaves nor sold for money. In the early 7th century, the first Sunni Muslim caliph, Abu Bakr, gave his army ten battlefield rules. He forbade treachery, the mutilation of dead bodies, and the killing of children, women, and the aged. He also said: Bring no harm to the trees, nor burn them with fire, especially those which are fruitful. Slay not any of the enemy's flock, save for your food. Early Christian writers held that Christians could not be soldiers at all. Augustine of Hippo contradicted them, writing about a just war doctrine that set out when war could or could not be morally justified. In 697, Adomnan of Iona gathered kings and church leaders from Ireland and Scotland to Birr. There he gave them the Law of the Innocents, banning the killing of women and children in war and the destruction of churches. Centuries later, alongside the chivalry of medieval Europe, the Roman Catholic Church promoted just war teachings reflected in movements like the Peace and Truce of God. That same impulse to shield non-combatants carried into the writings of Hugo Grotius.

• 3. The Golden Age

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  After the Thirty Years War, Europe entered what may be called the golden age of the jus in bello. For almost three centuries, the development of the modern law of nations placed positive constraints on how war was waged. International conflicts in Europe tended to be set piece battles fought by professional armies for limited and fixed political objectives. Civilians and civilian populations were usually left more or less unharmed by military forces. As the 19th century unfolded, the effort to codify the law of war and control the use of arms grew more earnest. There were profound hopes that war might eventually be abolished because civilization had become so advanced. Those hopes were tied to a belief that international adjudication and arbitration could replace war as a way to settle disputes. In 1864, twelve countries signed the Geneva Red Cross Convention, protecting hospital and ambulance crews. The historian Geoffrey Best called the period from 1856 to 1909 the law of war's epoch of highest repute. Its defining feature was a positive legal foundation, written down, superseding a regime grounded mainly in religion, chivalry, and custom. The international conference became the forum for debate, and the multilateral treaty became the mechanism for codification. Between 1899 and 1907, two Hague Peace Conferences produced detailed Hague Conventions. Tsar Nicholas II of Russia called the first in 1898, declaring that the moment was favorable for seeking a real and durable peace and for ending the progressive development of present armaments.

• 4. Three Wellsprings

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  Lawmaking treaties form the first of three principal sources of the modern law of war. These are conventions that bind consenting nations once they achieve widespread consent, and together they make up positive international humanitarian law. Custom forms the second source. Not all the law of war has been written into treaties, and the continuing importance of customary law is articulated by the Martens Clause. Such customary law is established by the general practice of nations together with their acceptance that the practice is required by law. Many of these customary rules were explored at the Nuremberg War Trials. General principles form the third source. As one statement puts it, certain fundamental principles provide basic guidance, including distinction, proportionality, and necessity, all part of customary international law and always applying to the use of armed force. A telling demonstration of how custom hardens came from the Nuremberg judgment on the law relating to war crimes and crimes against humanity. Decided under the Nuremberg Principles, it held that treaties like the Hague Convention of 1907, accepted by all civilised nations for about half a century, had become part of the customary laws of war. They were therefore binding on all parties, whether or not a party had signed the specific treaty. The reach of the law also begins early in particular conflicts. The Treaty of Armistice and Regularization of War, signed on the 25th and the 26th of November 1820 between Simon Bolivar of the Republic of Colombia and the Spanish commander Pablo Morillo, is regarded as the precursor of international humanitarian law.

• 5. Five Principles

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  Military necessity is the first of five principles most commonly cited as governing the legal use of force in armed conflict. It is bound by constraints: an attack must be intended to help defeat the enemy, must strike a legitimate military objective, and must not cause harm to civilians or civilian property that is excessive in relation to the concrete and direct military advantage anticipated. Distinction requires that belligerents separate combatants from protected civilians. Proportionality requires that the harm to protected civilians or their property not be excessive against the direct military advantage expected from an attack on a legitimate target. Robbie Sabel, professor of international law at the Hebrew University, has cautioned about how this works in practice. He notes that anyone with experience in armed conflict wants to hit the enemy harder than they hit you. As he puts it, if you are attacked with a rifle, there is no rule that you can only shoot back with a rifle, or that returning fire on one tank with two would be unfair. Humanity rests on the 1907 Hague Convention IV, which restricts arms, projectiles, or materials calculated to cause suffering manifestly disproportionate to the military advantage gained. In some countries, weapons are reviewed before combat to confirm they comply and are not designed to cause unnecessary suffering. Honor demands fairness and mutual respect between adversaries. Parties must accept that their right to injure each other is not unlimited, must not falsely claim the law's protections, and must recognize they fight not from personal hostility but on behalf of their States.

• 6. On The Battlefield

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  Section III of the Hague Convention of 1907 required hostilities to be preceded by a reasoned declaration of war or by an ultimatum carrying a conditional declaration. Later instruments worked against that requirement. Article 2 of the United Nations Charter of 1945, along with the older Kellogg-Briand Pact of 1928, sought to curtail the right of states to declare war at all. The result has been fewer modern conflicts opening with a formal declaration. Article 4(a)(2) of the Geneva Convention on prisoners of war defines a lawful combatant by four marks. Such a fighter must be commanded by a person responsible for subordinates, must bear a fixed distinctive sign recognizable at a distance, must carry arms openly, and must conduct operations in accordance with the laws and customs of war. Wearing the enemy's uniform to impersonate its combatants is possibly allowed, though the question is unsettled. Fighting in that uniform is unlawful perfidy, as is the taking of hostages. Protocol I, additional to the 1949 Geneva Conventions, forbids attacking persons parachuting from an aircraft in distress, wherever they may be over. Once they land in enemy-controlled territory, they must be given a chance to surrender unless they are plainly committing a hostile act or trying to escape. This protection does not extend to airborne troops, special forces, commandos, spies, saboteurs, liaison officers, or intelligence agents, who remain legitimate targets even when their aircraft is failing. The same body of law prohibits firing on a doctor, ambulance, or hospital ship displaying a Red Cross, Red Crescent, Magen David Adom, or Red Crystal. A person bearing a white flag, signaling an intent to surrender or communicate, must likewise be spared, so long as they keep their neutrality and commit no warlike act.

• 7. When The Rules Break

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  Reprisal is one answer the law gives to its own violation. During a conflict, punishment may take the form of a specific, deliberate, and limited violation of the laws of war in response to an enemy's breach. After a conflict ends, anyone who has committed or ordered a breach, especially atrocities, may be held individually accountable for war crimes. Nations that signed the Geneva Conventions are required to search for, try, and punish anyone responsible for certain grave breaches, an obligation set out in Articles 129 and 130 of the Third Geneva Convention. The law also binds individuals, not only states, including the members of armed forces. Combatants must make every effort to avoid harming people and property not involved in the war. Yet they commit no war crime if a bomb mistakenly or incidentally strikes a residential area. By contrast, combatants who deliberately use protected people or property as human shields or camouflage are responsible for the resulting harm. Fighters who break specific provisions are called unlawful combatants. Once captured, they may lose the protections owed to prisoners of war, but only after a competent tribunal, under Article 5 of the Third Geneva Convention, finds them ineligible for that status. Even then they keep certain protections. Under Article 5 of the Fourth Geneva Convention, they must be treated with humanity and, if tried, may not be deprived of the rights of fair and regular trial. One frontier remains unresolved. The use of contracted combatants and private security contractors so closely resembles state forces that it is unclear whether acts of war are being carried out by private or public agents, a question on which international law has yet to reach consensus.

• 8. A Living Code

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  Carla Del Ponte, chief prosecutor for the International Criminal Tribunal for the former Yugoslavia, made a forecast in 2001. There was no specific treaty ban on depleted uranium projectiles, she observed, but a developing scientific debate and concern about their effects. She suggested that international legal circles might one day reach a consensus that using such projectiles violates the general principles of law governing weapons in armed conflict. That openness to change runs through the whole field. Because the laws of war rest on consensus, with international law often relying on the self-policing of individual states, their content and interpretation are extensive, contested, and ever-changing. How a conflict is classified can itself decide who may lawfully use force, which sometimes leads to tactical classification so that one actor holds the sole right of force, and occasionally to a new body of law created for the purpose. That dynamic is visible in the assassination policies adopted during the war on terror. The treaty record keeps lengthening to match. The 1997 Ottawa Treaty banned anti-personnel mines, the 1998 Rome Statute created the International Criminal Court, and the 2017 Treaty on the Prohibition of Nuclear Weapons entered into force on the 22nd of January 2021. As conflicts change, so do the laws that govern them, and the next weapon or tactic to test those rules has not yet been named.