The Battle of Waterloo was fought on June 18, 1815, near the village of Waterloo, south of Brussels, in what is now Belgium. Napoleon Bonaparte, who had escaped from exile on the island of Elba in March 1815 and reclaimed power in France for the famous Hundred Days, faced an international coalition determined to remove him permanently. British forces under the Duke of Wellington (Arthur Wellesley), Prussian forces under Field Marshal Gebhard von Blücher, Dutch-Belgian forces, and reserves from other European allies confronted Napoleon's Armée du Nord. By evening on June 18, after hours of intense combat, the French army had been defeated. Casualties were heavy: French forces suffered 41,000 casualties (killed, wounded, or captured), while Allied forces sustained approximately 22,000 to 24,000 casualties. On June 19, 1815, the implications of this defeat unfolded across Europe.

Napoleon, recognizing the catastrophe, fled south from the battlefield toward Paris on June 19. His army, the disciplined force that had won battles across Europe for over a decade, was in complete disintegration. Soldiers scattered across the Belgian countryside; units ceased to exist as organized formations; panic replaced military order. Napoleon's hope of rallying the army around Paris and continuing to fight proved illusory. The political will to support him in France had collapsed. Within days, he would be forced to abdicate for the second and final time.

On the evening of June 18 and into June 19, Wellington and Blücher met briefly at the La Belle Alliance farmhouse on the battlefield. The meeting was short and businesslike. Wellington was exhausted after the day-long battle. Blücher, the 72-year-old Prussian commander, was physically worn but emotionally energized by victory. The two commanders, who had never been close, acknowledged the victory and coordinated the pursuit of Napoleon's remnants. Blücher urged more aggressive pursuit; Wellington, concerned about his own army's exhaustion and the control of his multinational force, counseled caution. The disagreement was minor; both understood that Napoleon's defeat was final.

Wellington, meticulous in administrative detail, composed his official Waterloo Dispatch on June 19, detailing the battle's course, the actions of various units, and the coordination with the Prussians. The dispatch, carried to London by Major Henry Percy, would be published in the London Gazette and distributed throughout the British Empire. In it, Wellington captured the emotional weight of command: "Nothing except a battle lost can be half so melancholy as a battle won." The quotation captured the terrible cost of victory—the thousands of young men dead or maimed, the widows and orphans that every victory created, the responsibility that weighed on military commanders for those losses.

The battlefield itself on June 19 presented a horrific scene. Bodies lay scattered across the muddy fields. Wounded men, crying out for help, lay in the rain and mud. The Household and Horse Guards units, which had suffered severely in cavalry charges on June 18, had left hundreds of dead horses and riders. Scottish regiments had been decimated; French Imperial Guard survivors were scattered, demoralized, and leaderless. The smell of death, blood, and gunpowder smoke hung over the field. Survivors of the battle staggered across the landscape, seeking water, food, shelter, and fellow soldiers.

Looting of the battlefield began immediately. Local Belgians, camp followers, and even soldiers from the victorious armies stripped the dead and dying of valuables, weapons, and equipment. Military discipline had largely broken down in the chaos. Wellington's officers struggled to restore order and organize burial and medical operations. The dead had to be buried quickly; the risk of disease was enormous. Mass graves were dug; many of the 3,000 to 5,000 dead would be buried in these pits without individual identification. Identification and notification of next of kin would take months or would never occur for many of the dead.

Medically, the situation on the battlefield was desperate. Field surgeons worked to treat the 10,000 or more wounded, using amputation as the primary treatment for severe wounds to the extremities. There was no anesthesia beyond alcohol. Chloroform and ether, while known to some military surgeons, were not widely available. Men faced amputation fully conscious, a trauma both physical and psychological that would haunt survivors for their remaining lives. Infection was inevitable; many men who survived the initial treatment would succumb to gangrene or sepsis in the days and weeks that followed.

News of the victory reached Paris on June 20 and spread rapidly across Europe. For Napoleon's supporters, the news was catastrophic. For the governments of Britain, Prussia, Austria, Russia, the Netherlands, and other allied powers, the news was triumphant but not surprising; the outcome had never been truly in doubt. Napoleon had mobilized some 200,000 troops; the Coalition had mobilized perhaps 700,000 across various theaters. The arithmetic of war had been unfavorable to Napoleon from the start.

On June 22, Napoleon abdicated for the second time. He wrote: "I have sacrificed my interests to those of the country... I depart. Let him [his son] be the rallying point of Frenchmen, and he may yet become a source of happiness to the world." His hope that his son might replace him in French government proved futile. The Allied powers would not permit any member of the Bonaparte family to hold power in France. The settlement would place the Bourbon monarchy back on the throne. Napoleon, now a prisoner and exile, would be transported to the island of St. Helena in the South Atlantic, thousands of miles from Europe, where he would spend his remaining years in confinement. He died in 1821.

June 19, 1815, marked the end of the age of Napoleonic warfare that had dominated European politics for over two decades. The Grande Armée, the instrument of French power and expansion, had ceased to exist. The order that would govern Europe for the next 40 years would be determined not by France but by the Concert of Europe—an arrangement between Britain, Prussia, Austria, and Russia designed to prevent any single power from achieving the kind of dominance that Napoleon had sought.