Thiệu Trị had passed over his more moderate eldest son Hồng Bảo, in favour of Tự Đức, known for his staunch Confucianism and opposition to foreigners and innovation.

As a result and due to the repressive policies of the previous emperor, there was now a great deal of dissatisfaction with Nguyễn rule and a legitimate royal figure for opposition to rally around.

He oppressed all foreigners in Vietnam, especially the Christian community, who had tried to overthrow his grandfather, such as in the Lê Văn Khôi revolt, calling their religion a "perverse doctrine".

The Christian mandarin Nguyễn Trường Tộ tried to convince Tự Đức that this was a suicidal policy, but he did not listen, confident that France was too involved with the chaos in Europe in 1848 to respond, but he was mistaken.

[5] Another Catholic official, Nguyễn Trường Tộ, had attempted forty-three times to persuade the court of Tu Duc to renovate the kingdom and adopt the changing global order.

In 1866 he was sent to Europe on the Vietnamese third mission to recruit technicians and teachers for a Western-style school foundation in Vietnam, but that project was also cancelled in 1867 when France annexed the rest of Cochinchina.

[7] In 2018 Lê Minh Khải claimed that he found two instances where the Tự Đức Emperor had ordered the Chinese edition of several classic books on science and industry from the West to be read by the mandarins and soldiers of the country.

The mountainous parts of Tonkin were territories of mainly indigenous Tai-speaking communities, and later Hmong, who were autonomous and lightly submissive in relations with the court of Hue.

[9] In 1860, the Chinese Muslim rebels were driven back, but the new White Flag army invaded Tonkin and laid Tụ Long abandoned by 1863, disrupting Vietnamese finance and the opium trade.

In 1865, after the fall of the Taiping Heavenly Kingdom, Liu Yongfu fled to China-Vietnam borders and founded the Black Flag Army, consisting of Chinese and Tai-Zhuang militia.

[13] New waves of Chinese rebels invaded Vietnam in form of the Yellow Flag Army, led by Wu Yazhong and later his lieutenant Pan Lunsi.

In March 1868, thousands of Yellow Flags crossed the borders and attacking local Vietnamese authorities and raiding grain warehouses in Cao Bằng.

The Nguyễn army fought bravely for some time, but their antiquated weapons and tactics were no match for the French, who suffered more from the climate and disease than from enemy resistance.

By an order of 1848 Tự Đức commanded all Vietnamese Catholic converts to renounce their religion, otherwise they would be branded on the face with the mark of a heretic and surrender all of their rights and privileges.

This caused a huge uproar, and many, such as the famous mandarin Trương Định, refused to recognize the treaty and fought on in defense of their country, denouncing Tự Đức for surrendering any part of their homeland.

Frustrated of being harassed by Tu Duc, Résident‐supérieur Rheinart France retaliated by barring Vietnam from joining the Paris International Fair, and from sending envoy to congratulate President Jules Grévy's inauguration.