Everyone says Napoleon's greatest mistake was Russia. Napoleon didn't. Years later, marooned on St. Helena with nothing left to protect, he named a different war. Spain. "That unfortunate war destroyed me." He called it the first cause of all the misfortunes of France. Here is what he actually did. In 1808, Spain was his ally. Not a rival, not a threat. An ally whose ports and armies he already had use of. He decided he wanted it outright anyway. He summoned the Spanish royal family to Bayonne, browbeat both the father and the son into signing away the crown, and handed the throne to his brother Joseph, a man who had never asked for it and did not want it. He expected the country to shrug. Spain had been governed badly for decades. He believed he was offering an upgrade. On the second of May, Madrid rose. French cavalry cleared the streets, and the next morning the firing squads went to work in the dark outside the city. Goya painted that night six years later, the man in the white shirt with his arms thrown out, and the image has outlived every dispatch Napoleon ever wrote. The rising did not stop in Madrid. It spread to towns with no garrison, no orders, and no plan. In July a French corps of roughly 18,000 men was surrounded in the heat at Bailén and surrendered in the open field to a Spanish army. Europe had spent a decade being told this could not happen. Austria read the news and started rearming. Then came the part that killed him slowly. Small bands, local men, no uniforms, hitting couriers and supply columns and stragglers and vanishing into country they had known since childhood. The Spanish called it the little war, guerrilla, and the word entered English in those years because English had no use for it before. A French soldier in Spain was safe in camp and nowhere else. Messages needed an escort of hundreds. Food had to be taken from people who would rather burn it. Meanwhile a British army under Wellington held on in Portugal and refused to be cornered. In 1810 he pulled behind the Lines of Torres Vedras, a belt of fortifications the French did not know existed until they walked up to them. Masséna sat in front of that wall through the winter and watched his army starve, then withdrew without a battle. By 1812 Napoleon had somewhere around a quarter of a million men tied down on the peninsula. That summer he crossed into Russia with the largest army Europe had ever seen and still left his best marshals and a fifth of his strength behind in Spain. In the same weeks he was burning through the Grande Armée at Borodino, Wellington broke a French army at Salamanca and rode into Madrid. June 1813, Vitoria. Joseph's army came apart and abandoned the treasury of the kingdom in the road. Wellington's men stopped to loot it and let the French escape. Beethoven wrote a piece about it. Weeks later Austria joined the coalition, and by 1814 there were British troops inside France coming up from the south while everyone else came from the east. Russia destroyed the army he had. Spain is the reason he never got another one, spent six years being bled by a country he did not need to fight, and handed his enemies the proof that he could lose.