This four-year campaign resulted in Emperor Tu Duc signing a treaty in June 1862, granting the French sovereignty over three provinces in the South.

The French eventually drove most of the Chinese troops out of Vietnam, but remaining groups in some Vietnamese provinces continued to resist France's control over Tonkin.

Although the treaty was never ratified, thousands of French mercenaries and officers rallied to the side of Nguyen Anh and campaigned against the Tay Son.

Although Lefèbvre was freed before the situation escalated, Lapierre, unaware of the news, opened fire and destroyed five Vietnamese ships in Da Nang Bay.

[4] Outraged by the French attack, Thiệu Trị ordered all European documents to be smashed, terminating all trade and terms with France, and put all foreign missionaries to be jailed and executed.

To intervene in Vietnam and also expand the French Empire, on 22 April 1857 Napoleon III created the Committee de la Cochinchine with Anatole, baron Brénier de Renaudière as its chairman, with the purpose of conquering Vietnam and capturing the Vietnamese monarch, using Tự Đức's persecution of Catholics and the undone treaty of 1787 as pretexts for the conquest.

In the same year, Tự Đức executed two Spanish Dominican priests; France and Spain declared war and launched the invasion of Vietnam.

[7] On 1 September 1858, a Franco-Spanish fleet of fourteen warships and 3,000 expeditionary troops, led by General Charles Rigault de Genouilly, launched attacks on Vietnamese positions in Danang.

[8] De Genouilly decided to abandon Danang to sail south for Saigon and the prosperous lower Mekong provinces-–the rice basket of Vietnam.

He assembled 2,000 troops and 14 warships and embarked for Saigon, destroyed several Vietnamese forts and coastal guns in Vung Tau, reaching the city on 17 February 1859.

Meanwhile, in the north, a Catholic bishop named Tạ Văn Phụng proclaimed himself to be a Lê prince, revolted against the Nguyen rule, and asked the French to aid his rebellion.

In February 1861, new French reinforcements of 3,500 troops and 70 warships led by General de Vassoigne arrived, broke through the Vietnamese line and captured the Ky Hoa citadel, six kilometers away from Saigon.

In June 1862, the Treaty of Saigon was signed, resulting in Vietnam losing three rich provinces, Gia Dinh, My Tho, Bien Hoa, and the Poulo Condore Island, and allowing religious freedom along with paying war reparations of 4 million Mexican pesos to France.

[17] In 1866, France convinced Tự Đức to hand over three remaining southwest provinces of Vĩnh Long, Hà Tiên, and Châu Đốc.

During the 1860s, pirates, bandits, remnants of the Taiping Rebellion in China, fled to Tonkin and turned Northern Vietnam into a hotbed for their raiding activities.

[19][20] These Chinese rebels eventually formed their own armies like the Black Flags of Liu Yongfu and cooperated with local Vietnamese officials, who now hired them as mercenaries instead of fighting them due to court power breakdown.

One of them, Jean Dupuis–a French merchant and explorer–decided to plot up the Red River with his own mercenaries and deliver arms to assist Ma Ju-lung in Yunnan fight against these rebels, but was objected by Vietnamese officials.

[23] In November, a French army consisting of 250 marines, sailors, and Cochinchina auxiliaries led by Francis Garnier arrived in Hanoi, with additional orders to demand that the river be opened up to foreign trade.

With support from local Vietnamese Catholics who saw the French as liberators, the attackers then captured several strongholds of the Red River Delta with ease.

In September, seventeen Chinese divisions (200,000 men) crossed the Sino-Vietnamese borders and occupied provinces north of the Red River.

In February 1883, Giorgios Vlavianos, the Greek-born British subject who had worked for Le Comte de Kergaradec, the French consul of Hanoi led the surrendered Yellow Flags to join Rivière.

[33] To knock the Hue court (who secretly funded the Black Flags) out of the war, the French Republic must force them to accept a new treaty.

"[36] On 25 August, two court officials Tran Dinh Tuc and Nguyen Trong Hop signed a twenty-seven-article treaty known as Harmand Accord.

French forces captured Bắc Ninh, Hưng Hóa, and Thái Nguyên citadels in March and April 1884, and arrived at Lạng Sơn in June.

It rallied Vietnamese scholar-officials and aristocracy class that were loyal to the crown and motivated by Confucian ethics to rebel against the establishing French colonial rule.

Anti-French and anti-Catholic Can Vuong rebellions raged across Tonkin and Annam; more than 40,000 Catholics, 18 French missionaries, 40 Vietnamese pastors were murdered; 9,000 churches were destroyed by angry mobs.

Hàm Nghi was betrayed by a Muong chief who asked for French troops to capture him in a refugee camp in November 1888 and was deported to Algeria.