Armies of the Eight-Nation Alliance capture Tientsin during the Boxer Rebellion.

The Eight-Nation Alliance was a multinational military coalition that invaded northern China in 1900 during the Boxer Rebellion, with the stated aim of relieving the foreign legations in Beijing, which were being besieged by the popular Boxer militiamen, who were determined to remove foreign imperialism in China. The allied forces consisted of about 45,000 troops from the eight nations of Germany, Japan, Russia, Britain, France, the United States, Italy, and Austria-Hungary. Neither the Chinese nor the quasi-concerted foreign allies issued a formal declaration of war.

The Siege of the International Legations was a pivotal event during the Boxer Rebellion in 1900, in which foreign diplomatic compounds in Peking were besieged by Chinese Boxers and Qing Dynasty troops. The Boxers, fueled by anti-foreign and anti-Christian sentiments, targeted foreigners and Chinese Christians, causing approximately 900 soldiers, sailors, marines, and civilians from various nations, along with about 2,800 Chinese Christians, to seek refuge in the Legation Quarter. The Qing government, initially ambivalent, ultimately supported the Boxers following international military actions. The siege lasted 55 days, marked by intense combat and a brief truce, until an international relief force arrived from the coast, defeated the Qing forces, and lifted the siege. The failure of the siege and the subsequent occupation of Peking by foreign powers significantly weakened the Boxer Rebellion, leading to its eventual suppression, and increased foreign influence and intervention in China.

Tianjin is a direct-administered municipality in northern China on the shore of the Bohai Sea. It is one of the nine national central cities, with a total population of 13,866,009 inhabitants at the time of the 2020 Chinese census. Its metropolitan area, which is made up of 12 central districts, was home to 11,165,706 inhabitants in 2015 and is also the world's 29th-largest agglomeration and 11th-most populous city proper.