The crisis began when the Boxers, a populist peasant movement determined to expel foreign influence from China, attacked missionaries, foreign nationals, and Chinese Christians across the north in 1899 and 1900. The Qing government, under the Manchu general Ronglu, threw its support behind the Boxers and besieged the Legation Quarter in Beijing. For 55 days, from June 20 to August 14, 1900, some 473 foreign civilians, 409 soldiers from eight countries, and approximately 3,000 Chinese Christians held out inside the compound. Simultaneously, the North Cathedral -- the Beitang -- endured its own siege, defended by 43 French and Italian soldiers, 33 Catholic priests and nuns, and about 3,200 Chinese Catholics who suffered from starvation and underground mines detonated beneath them.

On August 14, 1900, the allied forces marched from Tianjin to relieve the siege. Japan provided the largest contingent, with over 20,000 troops, followed by Russia with 12,400. The Japanese troops fought aggressively -- at Tianjin, they suffered more than half the allied casualties while making up less than a quarter of the force. Britain contributed 10,000 soldiers, many drawn from Indian regiments of Baluchis, Sikhs, Gurkhas, and Punjabis. Germany dispatched an expeditionary corps of about 15,000 under General Alfred von Waldersee, though most arrived too late for the major engagements. The United States drew on forces already deployed in the Philippines after the Spanish-American War. Even future president Herbert Hoover was present during the siege, helping build barricades while his wife Lou nursed the wounded and carried a Mauser pistol.

What followed the liberation was devastating. Allied troops looted the Forbidden City, the Summer Palace, government buildings, and temples with systematic thoroughness. More than 3,000 gold-plated bronze Buddhas were taken from Songzhu Temple alone. Soldiers scraped gold plating from the copper tanks outside the Forbidden City's palaces -- scratch marks still visible today. The Yongle Dadian, an encyclopedic masterwork compiled by approximately 2,169 scholars during the Ming dynasty between 1403 and 1408 and comprising 22,937 chapters, had already been partially damaged in the Second Opium War. In 1900, the alliance destroyed what remained. Parts of the encyclopedia were reportedly used to build fortifications. Troops executed unknown numbers of suspected Boxers in the countryside. A U.S. Marine later wrote that he witnessed German and Russian soldiers committing atrocities against civilians.

Empress Dowager Cixi and the imperial court fled to Xi'an, sending Li Hongzhang to negotiate. The fighting ended in 1901 with the Boxer Protocol, which imposed crushing indemnities, granted foreign powers the right to station troops on Chinese soil, and deepened the humiliation that would fuel revolutionary sentiment for decades. Russia used the crisis to seize effective control of Manchuria. Italy obtained a concession area in Tianjin. The alliance's members returned to being rivals, as they had been before the Boxers forced them into temporary cooperation. China remembered the invasion as a defining wound -- a moment when eight of the world's most powerful nations descended on a weakened empire and stripped it of treasures, sovereignty, and dignity.