Vietnam cedes Biên Hòa, Gia Định and Định Tường to France

Background. The treaty resulted from the Cochinchina campaign, a military operation launched by France and Spain against the Nguyễn state between 1858 and 1862. French forces faced initial difficulties but gained momentum after the Battle of Ky Hoa in 1861. The fall of Mỹ Tho and Biên Hòa, along with the capture of Vĩnh Long in March 1862, severely worsened the strategic situation for the Huế court, prompting Emperor Tự Đức to seek peace.

Negotiations. In May 1862, preliminary discussions occurred at Huế, followed by meetings off Tourane. Tự Đức's minister Phan Thanh Giản signed the treaty on 5 June 1862 with Admiral Bonard and Spanish representative Colonel Carlos Palanca Gutiérrez. The treaty was later confirmed by the Treaty of Huế in April 1863, which also addressed port access and foreign affairs control.

Aftermath. The ceded provinces became the basis of the French colony of Cochinchina, formally constituted in 1864. The treaty was viewed as a national humiliation by the court and people. Guerrilla leader Trương Định refused to recognize the treaty, breaking with the Nguyễn army and forming a self-defense movement. The court later sought revisions, but Vice-Admiral Bonard noted the peace was not faithfully executed.