<P> French policy four years later saw a reversal, with the French continuing to accumulate territory . In 1862, France obtained concessions from Emperor Tự Đức, ceding three treaty ports in Annam and Tonkin, and all of Cochinchina, the latter being formally declared a French territory in 1864 . In 1867 the provinces of Châu Đốc, Hà Tiên and Vĩnh Long were added to French - controlled territory . </P> <P> In 1863, the Cambodian king Norodom had requested the establishment of a French protectorate over his country . In 1867, Siam (modern Thailand) renounced suzerainty over Cambodia and officially recognised the 1863 French protectorate on Cambodia, in exchange for the control of Battambang and Siem Reap provinces which officially became part of Thailand . (These provinces would be ceded back to Cambodia by a border treaty between France and Siam in 1906). </P> <P> France obtained control over northern Vietnam following its victory over China in the Sino - French War (1884--85). French Indochina was formed on 17 October 1887 from Annam, Tonkin, Cochinchina (which together form modern Vietnam) and the Kingdom of Cambodia; Laos was added after the Franco - Siamese War in 1893 . </P> <P> The federation lasted until 21 July 1954 . In the four protectorates, the French formally left the local rulers in power, who were the Emperors of Vietnam, Kings of Cambodia, and Kings of Luang Prabang, but in fact gathered all powers in their hands, the local rulers acting only as figureheads . </P>

What event made france feel justified in invading indochina