Tonkin Campaign: French forces capture the Sơn Tây citadel.

The Tonkin campaign was an armed conflict fought between June 1883 and April 1886 by the French against, variously, the Vietnamese, Liu Yongfu's Black Flag Army and the Chinese Guangxi and Yunnan armies to occupy Tonkin and entrench a French protectorate there. The campaign, complicated in August 1884 by the outbreak of the Sino-French War and in July 1885 by the Cần Vương nationalist uprising in Annam, which required the diversion of large numbers of French troops, was conducted by the Tonkin Expeditionary Corps, supported by the gunboats of the Tonkin Flotilla. The campaign officially ended in April 1886, when the expeditionary corps was reduced in size to a division of occupation, but Tonkin was not effectively pacified until 1896.

The French Third Republic was the system of government adopted in France from 4 September 1870, when the Second French Empire collapsed during the Franco-Prussian War, until 10 July 1940, after the Fall of France during World War II led to the formation of the Vichy government. The French Third Republic was a parliamentary republic.

The Sơn Tây campaign was a campaign fought by the French to capture the strategically important city of Sơn Tây in Tonkin from Liu Yongfu's Black Flag Army and allied contingents of Vietnamese and Chinese troops. The campaign was one of several clashes between the Tonkin Expeditionary Corps and the Black Flag Army during the Tonkin campaign (1883–1886), and took place during the period of undeclared hostilities that preceded the Sino-French War.

Sơn Tây is a suburban ward of Hanoi the capital of Vietnam in the Red River Delta of Vietnam.