Rules for War How Humanity Tried to Limit Its Worst Impulse

On a June morning in 1859, a Swiss businessman named Henry Dunant rode toward the small northern Italian town of Solferino expecting to conduct a meeting. What he found instead would haunt him for the rest of his life and change the course of history.

The Battle of Solferino had just ended. Nearly three hundred thousand soldiers from France, Austria, and the Kingdom of Sardinia had clashed in what would become one of the bloodiest single-day engagements of the nineteenth century. Forty thousand men lay dead or wounded across the fields and hillsides. Dunant, who had no military or medical training, wandered among the bodies for hours. Wounded men begged for water. Others died where they had fallen, untreated, unidentified, with no one to document that they had ever existed. The Austrian and French field hospitals were so overwhelmed that surgeons performed amputations without anesthesia in open farmhouses, the floors slick with blood. Local villagers had begun burying the dead in mass graves before the dying had finished dying.

Dunant did what he could. He organized local women to carry water and dress wounds. He sent for emergency supplies. And he told the women something that would echo across generations: treat all the wounded, he said, regardless of which side they had fought on. Tutti fratelli. All brothers.

That phrase captures something profound about the paradox at the heart of this episode. Humanity has always gone to war. But humanity has also always, in some form, insisted that even war has rules. That paradox — the impulse to destroy coexisting with the impulse to limit destruction — is one of the most revealing things about us as a species.

Today, we trace the long, turbulent, and often contradictory history of how the laws of war were born. From ancient sacred texts to medieval battlefields to the legal architecture that now governs every armed conflict on Earth, this is the story of humanity's attempt to civilize its worst impulse. And it is also a story about what that attempt reveals about human nature itself.