The Laws of War: A Brief History of Humanity in Conflict

International Humanitarian Law (IHL), often known simply as the laws of war or the law of armed conflict, is the grand, and perhaps paradoxical, human attempt to impose limits on brutality itself. It is a specialized body of international rules, born from the crucible of conflict, that seeks to regulate the conduct of warring parties and to mitigate the suffering of those caught in the crossfire. At its core, IHL operates on a fundamental premise: that even when diplomacy fails and nations resort to arms, a bedrock of shared humanity must remain. It does not concern itself with why a war begins (a domain known as jus ad bellum), but rather with how it is fought (jus in bello). This intricate legal architecture is built upon two towering pillars: first, the protection of those who are not, or are no longer, participating in the hostilities—such as civilians, wounded soldiers, and prisoners of war; and second, the restriction of the means and methods of warfare, prohibiting weapons and tactics that are inherently indiscriminate or cause superfluous injury and unnecessary suffering. It is a code of conduct for the battlefield, a thin red line of principle drawn in the blood-soaked sand of human history.

The story of International Humanitarian Law does not begin in the marbled halls of Geneva or The Hague, but in the whispers of conscience that echo from the dawn of organized civilization. As long as humans have waged war, they have been haunted by the need to justify it and, in doing so, to define its limits. This impulse, to separate permissible violence from unconscionable atrocity, is not a modern invention but a recurring theme woven through the cultural tapestry of our species. It is a testament to the inherent tension between our capacity for tribal aggression and our yearning for a universal moral order.

In the ancient world, these rules were rarely codified in international treaties; instead, they were embedded in religion, honor codes, and military custom. The Hittite Code, dating back to the 16th century BCE, prescribed more humane treatment for prisoners of war than many of its contemporaries. In ancient India, the epic poem Mahabharata describes elaborate rules for the Kurukshetra War, forbidding warriors from attacking an unarmed or surrendering enemy, a non-combatant, or someone who was fleeing. These rules, while perhaps more mythic than historically practiced, reveal a deep-seated cultural ideal of honorable combat. Similarly, the Chinese general Sun Tzu, in his 6th-century BCE masterpiece, The Art of War, advises that a surrounded enemy must be given an avenue of escape, not out of mercy, but out of a pragmatic understanding that a cornered foe fights with desperate, unpredictable ferocity. He also speaks of treating captured soldiers well, a tactic aimed at encouraging defections and winning hearts and minds. Across the globe, similar ethical frameworks emerged from religious traditions. The Old Testament contains rules for siege warfare, such as the Deuteronomic command to spare fruit-bearing trees, a primitive form of protecting civilian property essential for survival. Later, the rise of Islam in the 7th century CE brought with it a sophisticated code of conduct for war, derived from the teachings of the Prophet Muhammad. Islamic law strictly forbade the killing of women, children, and the elderly; the destruction of crops and livestock; and the mutilation of the dead. These early laws were not “international” in the modern sense—they were typically binding only upon those within a specific cultural or religious sphere—but they were the foundational stones. They established the critical precedent that warfare was not a lawless vacuum, but a human activity that could, and should, be subject to ethical and spiritual restraint.

The Roman Empire, with its genius for law and administration, further developed these concepts. Roman jurists began to articulate the idea of jus gentium, a “law of nations” that applied not just to Roman citizens but to all peoples. Within this framework, they developed doctrines around the idea of a bellum justum, or “just war.” While primarily focused on the reasons for going to war, this concept also touched upon its conduct. Philosophers like Cicero argued that faith must be kept even with the enemy, laying an early foundation for the sanctity of treaties and truces. These were not humanitarian laws as we know them, for Rome could be an exceptionally brutal conqueror. Yet, the very existence of these legal and philosophical debates demonstrates a profound shift: the act of war was being brought from the realm of pure might into the world of intellectual and moral scrutiny. This Roman legacy, preserved and later studied in medieval Europe, would provide the essential vocabulary for the thinkers who would one day build the formal edifice of IHL.

As the Western Roman Empire crumbled and Europe entered the Middle Ages, the nascent idea of a universal law of war fragmented. For centuries, conflict was localized, brutal, and governed more by the sword than by the pen. Yet, even in this era of iron, new seeds of restraint began to sprout, cultivated not in law schools, but in the codes of warrior aristocracies and, later, in the studies of Renaissance philosophers who dared to dream of a more orderly world.

Out of the chaos of feudal warfare arose the code of Chivalry. This was not a legal system but a cultural ethos, a blend of martial prowess, piety, and courtly manners that defined the ideal knight. While often romanticized, chivalry contained a rudimentary set of rules for combat. It dictated that knights should protect the weak and defenseless—specifically, the church, women, and the poor. It demanded that a captured knight be treated as an honored guest, to be ransomed rather than killed, a practice driven as much by economic pragmatism as by noble principle. Tournaments, elaborate mock battles, served as a training ground not just for war but for its rules. However, the protections of chivalry were almost exclusively a matter of class. This gentleman's agreement applied to fellow knights, to members of the same aristocratic warrior caste. The common foot soldier or the peasant whose fields were razed enjoyed no such courtesies. The brutal sack of a city, with its attendant massacre and pillage, was a common feature of medieval warfare. Chivalry was a crucial step in humanizing conflict, but its humanity was selective. It affirmed the principle that rules were possible, but it had not yet made the leap to the universal application of those rules.

The true intellectual revolution arrived with the Renaissance and the Enlightenment, as scholars began to build a secular, rational foundation for international relations. The Dutch jurist Hugo Grotius (1583-1645) stands as a giant in this transition. Witnessing the horrific brutality of the Thirty Years' War, a conflict that devastated central Europe, Grotius wrote his magnum opus, De Jure Belli ac Pacis (On the Law of War and Peace) in 1625. In this monumental work, he painstakingly separated international law from theology, arguing that a “law of nations” existed and would be valid even if God did not exist. He systematically analyzed the customs of war from ancient times to his own, distinguishing between lawful and unlawful acts and arguing for moderation. Grotius was the first to create a comprehensive, systematic treaty on international law, earning him the title “Father of International Law.” Following Grotius, Enlightenment philosophers refined these ideas. Jean-Jacques Rousseau, in his 1762 work The Social Contract, made a conceptual leap that would become a cornerstone of modern IHL. He argued that war is not a relationship between man and man, but between State and State. Soldiers are enemies only by accident, as defenders of their state. Once they lay down their arms and surrender, “they cease to be enemies or instruments of the enemy, and become once more merely men, and no one has any longer a right to their lives.” This was a revolutionary idea. It drew a bright line between the state's military apparatus and the individual human beings who comprised it, and by extension, between combatants and the civilian population. The philosopher's quill had articulated the principle that would one day shield millions.

For all the profound thinking of Grotius and Rousseau, the laws of war remained a matter of philosophy and custom, not binding international treaty. The battlefield remained a place of unmitigated horror. It would take the cataclysm of industrial warfare, witnessed through the eyes of one compassionate and determined individual, to transform these abstract principles into a global humanitarian movement and a concrete body of law.

On June 24, 1859, the armies of the Austrian Empire and the Franco-Sardinian Alliance clashed near the small Italian town of Solferino. It was a battle of unprecedented scale and ferocity, a grim harbinger of the wars to come. For over fifteen hours, some 300,000 men fought with a terrifying new efficiency, armed with rifled muskets and cannons that were far more accurate and deadly than their predecessors. When the fighting finally ceased, the field was left strewn with over 40,000 dead and wounded soldiers. By sheer chance, a Swiss businessman named Henry Dunant was traveling in the area and arrived on the scene in the battle's immediate aftermath. What he saw scarred him for life. The official army medical services were completely overwhelmed, possessing neither the staff, the training, nor the supplies to handle a disaster of this magnitude. Thousands of men—Austrian, French, and Italian alike—were left lying on the field, crying out in agony from horrific wounds, slowly dying of shock and infection under the blistering summer sun. Dunant was appalled not only by the suffering but by the utter abandonment of these men. Moved by a profound sense of human duty, he sprang into action. He organized the local townspeople, primarily women, to help, establishing makeshift hospitals in churches and private homes. He pleaded with them to tend to all the wounded, regardless of their nationality, coining the immortal phrase “Tutti fratelli” (All are brothers). For days, Dunant and his volunteers worked tirelessly, bringing water, binding wounds, and offering what comfort they could to the dying.

The experience at Solferino never left him. Upon returning to Geneva, Henry Dunant wrote a short but powerful book, published in 1862, titled A Memory of Solferino. It was a masterpiece of eyewitness reportage and passionate advocacy. He did not simply recount the horrors he had seen; he proposed a radical solution. He asked two world-changing questions:

• First: “Would it not be possible, in time of peace and quiet, to form relief societies for the purpose of having care given to the wounded in wartime by zealous, devoted and thoroughly qualified volunteers?”
• Second: “Could not advantage be taken of a Congress… to formulate some international principle, sanctioned by a Convention inviolate in its character, which, once agreed upon and ratified, might constitute the basis for societies for the relief of the wounded in the different countries of Europe?”

The book was an immediate sensation. Dunant sent copies to the crowned heads, military leaders, and philanthropists of Europe. His graphic depiction of suffering, combined with his clear, practical proposals, struck a powerful chord in a society that was beginning to grapple with the social and moral consequences of industrialization.

Dunant's call to action found fertile ground in his home city of Geneva. With four other prominent Genevan citizens, he formed the “Committee of Five,” which in 1863 became the International Committee for Relief to the Wounded, the body that would soon be known as the International Committee of the Red Cross (ICRC). Their energy was formidable. Just one year later, in 1864, the Swiss government, at the committee's urging, convened a diplomatic conference. Twelve nations attended and, in a remarkably short time, signed the first Geneva Convention for the Amelioration of the Condition of the Wounded in Armies in the Field. This document was revolutionary. For the first time in history, nations agreed to a binding, international treaty that established rules for the care of the victims of war. It declared that wounded and sick soldiers were to be considered neutral and must be collected and cared for, regardless of their side. It established the neutrality of medical personnel, hospitals, and ambulances, granting them protection to carry out their work. And it adopted the red cross on a white background—the reverse of the Swiss flag—as a protective emblem to identify them. The abstract idea of humanity in war was finally codified into law. A single man's conscience had ignited a global revolution.

The first Geneva Convention was a monumental achievement, but it was only a beginning. It focused exclusively on the wounded soldier on the battlefield. The broader conduct of war—the weapons that could be used, the targets that could be attacked, the rights of prisoners—remained governed by unwritten custom. As the 19th century drew to a close, a parallel legal track emerged, one that sought not just to care for the victims of war, but to regulate the very means and methods of its violence.

This new development was championed by an unlikely source: Tsar Nicholas II of Russia. Alarmed by the spiraling arms race among the Great Powers, he called for an international peace conference at The Hague in the Netherlands in 1899. While the conference failed in its primary goal of disarmament, it succeeded in codifying the existing customs of land warfare into a series of treaties known as the Hague Conventions. A second conference in 1907 expanded upon these rules. The Hague Conventions established the crucial legal distinction between combatants and civilians, and the principle that civilians and their property may not be the object of attack. They forbade the use of certain weapons, including projectiles that spread “asphyxiating or deleterious gases” and bullets that expand or flatten easily in the human body (so-called “dum-dum” bullets). They laid out detailed rules for the treatment of prisoners of war and the administration of occupied territory. With this, the two main streams of IHL were established:

• “Geneva Law”: Focused on protecting the victims of conflict (the wounded, sick, shipwrecked, and prisoners of war).
• “Hague Law”: Focused on regulating the means and methods of combat (the weapons, tactics, and permissible targets).

Together, they represented a high-water mark of late 19th-century optimism, a belief that even the scourge of war could be civilized through reason and international agreement. This optimism was about to be shattered.

World War I (1914-1918) was the first industrial, “total” war. It was a brutal crucible that tested the new laws of war to their breaking point, and in many cases, beyond. The machine gun, heavy artillery, and trench warfare produced casualties on a scale that dwarfed Solferino. The Hague Conventions' ban on poison gas was flagrantly violated by both sides, leading to a new kind of chemical horror on the battlefield. The vast naval blockades aimed to starve entire enemy populations into submission, blurring the line between civilian and combatant. Yet, the law did not vanish entirely. The ICRC expanded its operations massively, visiting prisoner-of-war camps on both sides and facilitating the exchange of mail and information between millions of prisoners and their families. While the treatment of POWs varied wildly, the existence of the Geneva Convention and the oversight of the ICRC arguably prevented far worse abuses. The Great War was a devastating demonstration of the law's fragility, but also of its enduring necessity. It revealed loopholes and weaknesses, particularly the lack of any explicit protection for civilians, that would have to be addressed.

If World War I was a failure of the law, World War II (1939-1945) was its negation. The conflict was defined by ideologies that rejected the very concept of a shared humanity. The principle of civilian immunity, enshrined in Hague Law, was systematically dismantled by all sides through the strategic bombing of cities like London, Dresden, and Tokyo. On the Eastern Front and in the Pacific, the norms for treating prisoners of war were often ignored, leading to the death of millions through starvation, disease, and summary execution. And then there was the Holocaust, a state-organized program of genocide that represented a complete collapse of legal and moral restraint. It was a crime so vast and systematic that it fell outside the traditional framework of the laws of war, prompting the jurist Raphael Lemkin to coin a new term: genocide. The war revealed that the existing conventions, written in a more genteel age, were utterly inadequate to confront a form of warfare aimed not merely at defeating an enemy state, but at annihilating entire peoples. The abyss had been stared into, and the world recoiled in horror. It was clear that the laws of war had to be rebuilt, stronger and more comprehensive than ever before.

The end of World War II left a world in ruins, but also one possessed by a fierce determination: never again. This sentiment fueled an unprecedented period of international legal construction. The international community, sobered by the horrors it had witnessed, came together not just to punish the perpetrators of atrocities but to create a new legal architecture that would be robust enough to prevent their recurrence. This was the moment modern International Humanitarian Law was truly born.

The first order of business was accountability. Between 1945 and 1946, the victorious Allied powers established an International Military Tribunal in the German city of Nuremberg to prosecute the highest-ranking Nazi leaders. The Nuremberg Trials were a watershed moment. For the first time in history, an international court held individuals criminally responsible for their actions during a war. The defense that one was “just following orders” was rejected as a justification for committing atrocities. The defendants were charged with “war crimes” (violations of the traditional laws of war), “crimes against peace” (the act of waging an aggressive war), and a new category, “crimes against humanity,” which included acts like murder, extermination, and enslavement committed against any civilian population. The Nuremberg Trials established a revolutionary principle: sovereignty was not a license to commit mass murder. The law of nations could pierce the veil of the state and hold individuals to account. This principle of individual criminal responsibility became the capstone of IHL, transforming it from a set of rules for states into a code of conduct for every soldier on the battlefield.

The next, and perhaps greatest, task was to rewrite the laws themselves. In 1949, at a diplomatic conference in Geneva, the international community adopted four new Geneva Conventions. This was not a minor revision; it was a complete overhaul and a massive expansion of humanitarian law, directly informed by the bitter lessons of the preceding decades. The Four Conventions remain the bedrock of IHL to this day:

• First Convention: Protects wounded and sick soldiers on land. (An update of the original 1864 Convention).
• Second Convention: Protects wounded, sick, and shipwrecked military personnel at sea.
• Third Convention: Protects prisoners of war. It vastly expanded on earlier Hague rules, detailing precise requirements for housing, food, medical care, and communication with their families.
• Fourth Convention: This was the most significant innovation. For the first time, a comprehensive treaty was dedicated entirely to the protection of civilians in times of war, including in occupied territory. It forbids murder, torture, collective punishment, and the taking of hostages, and it strictly regulates the powers of an occupying force.

Crucially, all four conventions share a Common Article 3, a miniature treaty-within-a-treaty that applies basic humanitarian protections to “armed conflicts not of an international character”—in other words, civil wars. This was a radical step, extending the reach of international law into the internal affairs of states.

By the 1960s and 1970s, the nature of warfare was changing again. The age of decolonization and the Cold War saw a proliferation of wars of national liberation and internal conflicts. To address this, two Additional Protocols to the Geneva Conventions were adopted in 1977.

• Protocol I: Relates to international armed conflicts and provides a major update to Hague Law. It strengthened the protection of civilians by providing a more precise definition of military objectives and explicitly prohibiting indiscriminate attacks and attacks on civilian infrastructure like dams and nuclear power plants.
• Protocol II: Was the first-ever international treaty devoted exclusively to the victims of non-international armed conflicts. It expanded on Common Article 3, strengthening protections for persons deprived of their liberty and prohibiting attacks on civilians in civil wars.

With the 1949 Conventions and the 1977 Protocols, the modern legal edifice of IHL was largely complete. It was a comprehensive, universal code that, in theory, covered almost every aspect of armed conflict and protected every category of victim. The challenge, as always, would be in its application.

The codification of IHL in the mid-20th century was a triumph of the human spirit, an assertion of universal values in the face of unparalleled destruction. Yet, law is not static. It must breathe, adapt, and confront the ever-changing realities of the world it seeks to govern. The story of IHL in the late 20th and early 21st centuries is one of implementation, expansion, and a constant struggle to remain relevant in a world of new technologies, new actors, and new types of conflict.

For decades, the principle of individual accountability established at the Nuremberg Trials was more of an ideal than a reality. That changed dramatically in the 1990s. The horrific genocides in the former Yugoslavia and Rwanda spurred the UN Security Council to create ad hoc international criminal tribunals to prosecute the perpetrators. These tribunals revived the spirit of Nuremberg, holding dozens of political and military leaders accountable for their crimes and creating a rich body of jurisprudence that clarified and strengthened many provisions of IHL. The success of these tribunals fueled a long-standing dream: the creation of a permanent court to combat impunity. In 2002, that dream became a reality with the establishment of the International Criminal Court (ICC) in The Hague. The ICC is a court of last resort, designed to step in only when national legal systems are unable or unwilling to prosecute the most serious international crimes: genocide, crimes against humanity, and war crimes. While its jurisdiction is not universally accepted and it faces immense political challenges, its very existence serves as a powerful deterrent and a symbol that the world will not turn a blind eye to atrocity.

The 21st-century battlefield bears little resemblance to Solferino. Conflicts are rarely clear-cut wars between nation-states. Instead, they are often asymmetrical struggles involving non-state armed groups, counter-terrorism operations, and foreign interventions in complex civil wars. This new landscape poses profound challenges to a legal framework designed for conventional armies.

• Non-State Actors: How does IHL apply to groups like Al-Qaeda or ISIS, which do not respect the law and whose members often blend in with the civilian population? While the law is clear that all parties to a conflict are bound by IHL, ensuring compliance from such groups is a monumental task.
• Cyber Warfare: Can a cyber-attack on a country's electrical grid or banking system constitute an “armed attack” under IHL? If it leads to civilian deaths (e.g., in hospitals that lose power), could it be a war crime? Jurists are currently grappling with how to apply principles written for physical warfare to the digital domain.
• Autonomous Weapons: The development of “killer robots”—weapons systems that can independently select and engage targets without meaningful human control—raises fundamental legal and ethical questions. Can a machine ever be programmed to comply with the complex, judgment-based rules of distinction and proportionality?

These challenges demonstrate that IHL is not a finished monument, but a living, evolving conversation. It is constantly being debated, interpreted, and re-affirmed by states, courts, the ICRC, and civil society. The history of International Humanitarian Law is a story of a persistent, stubborn, and often frustrated struggle. It is a law that is violated every day, in every conflict around the world. And yet, its power does not lie in its perfect enforcement, but in its enduring existence. It provides a universal standard of conduct, a language for condemning brutality, and a legal framework for holding perpetrators to account. It ensures that medical workers can save lives, that prisoners are not forgotten, and that civilians are shielded from the worst of the violence. It is a testament to our species' remarkable and hopeful insistence that even in the midst of our most destructive impulses, we must never lose sight of our shared humanity.