Treaty of Saigon
For a series of complex reasons, the Second French Empire of Napoleon III, with the help of Spanish troops arriving from the Spanish East Indies, attacked Đà Nẵng (Tourane) of Nguyen Dynasty Vietnam in September 1858. Unable to occupy Đà Nẵng, the alliance moved to Lower Cochinchina in the South. On 17 February 1859, they captured Saigon. Later on, the French defeated the Nguyễn army at the Battle of Ky Hoa in 1861. The Vietnamese government was forced to cede the three southern Vietnamese provinces of Biên Hòa, Gia Định and Định Tường to France in June 1862 Treaty of Saigon.