[citation needed] French explorers followed the course of the Red River through northern Vietnam to its source in Yunnan, arousing hopes for a profitable trade route with China that could bypass the treaty ports of the Chinese coastal provinces.

[24] The Vietnamese government, unable to confront Rivière with its own ramshackle army, once again enlisted the help of Liu Yongfu, whose well-trained and seasoned Black Flag soldiers would prove a thorn in the side of the French.

In April 1883, realising that the Vietnamese lacked the means of resisting the French effectively, the Chinese civil Mandarin Tang Jingsong (唐景崧) persuaded Liu Yongfu to take the field against Rivière with the Black Flag Army.

Rivière's small force (around 450 men) attacked a strong Black Flag defensive position near the village of Cầu Giấy, a few miles to the west of Hanoi, known to the French as Paper Bridge (Pont de Papier).

[33] Jules Ferry and the French foreign minister Paul-Armand Challemel-Lacour met a number of times in the summer and autumn of 1883 with Marquis Zeng in Paris, but these parallel diplomatic discussions also proved abortive.

[39][independent source needed] The defeat at Bắc Ninh, coming close on the heels of the fall of Sơn Tây, strengthened the hand of the moderate element in the Chinese government and temporarily discredited the extremist 'Purist' party led by Zhang Zhidong, which was agitating for a full-scale war against France.

The French assumed that the Chinese troops would leave Tonkin as agreed, and made preparations for occupying the border towns of Lạng Sơn, Cao Bằng and Thất Khê.

In a two-hour engagement watched with professional interest by neutral British and American vessels (the battle was one of the first occasions on which the spar torpedo was successfully deployed), Courbet's Far East Squadron annihilated China's outclassed Fujian fleet and severely damaged the Foochow Navy Yard (which, ironically, had been built under the direction of the French administrator Prosper Giquel).

[45] Meanwhile, the French decided to put pressure on China by landing an expeditionary corps in northern Formosa to seize Keelung and Tamsui, redeeming the failure of 6 August and finally winning the 'pledge' they sought.

Although severely outnumbered, the French captured a number of minor Chinese positions to the southeast of Keelung at the end of January 1885, but were forced to halt offensive operations in February due to incessant rain.

On 11 February Courbet's task force met the cruisers Kaiji, Nanchen and Nanrui, three of the most modern ships in the Chinese fleet, near Shipu Bay, accompanied by the frigate Yuyuan and the composite sloop Chengqing.

The French government retaliated by ordering Courbet to implement a 'rice blockade' of the Yangzi River, hoping to bring the Qing court to terms by provoking serious rice shortages in northern China.

In late September 1884, large detachments of the Guangxi Army advanced from Langson and probed into the Lục Nam valley, announcing their presence by ambushing the French gunboats Hache and Massue on 2 October.

Brière de l'Isle responded immediately, transporting nearly 3,000 French soldiers to the Lục Nam valley aboard a flotilla of gunboats and attacking the Chinese detachments before they could concentrate.

In the wake of these French victories the Chinese fell back to Bắc Lệ and Đồng Sông, and de Négrier established important forward positions at Kép and Chũ, which threatened the Guangxi Army's base at Lạng Sơn.

The French also sealed off the eastern Delta from raids by Chinese guerillas based in Guangdong by occupying Tiên Yên, Đông Triều and other strategic points, and by blockading the Cantonese port of Beihai (Pak-Hoi).

The debate culminated in Campenon's resignation and his replacement as army minister by the hawkish General Jules Louis Lewal, who immediately ordered Brière de l'Isle to capture Lạng Sơn.

On 12 February, in a costly but successful battle, the Turcos and marine infantry of Colonel Laurent Giovanninelli's 1st Brigade stormed the main Chinese defences at Bắc Việt, several kilometres to the south of Lạng Sơn.

[52][independent source needed] On 13 February, the French column entered Lạng Sơn which the Chinese abandoned after fighting a token rearguard action at the nearby village of Kỳ Lừa.

The Tuyên Quang garrison, 400 legionnaires and 200 Tonkinese auxiliaries under the command of chef de bataillon Marc-Edmond Dominé, beat off all attempts to storm their positions, but lost over a third of their strength (50 dead and 224 wounded) sustaining a heroic defence against overwhelming odds.

The brigade, reinforced at Phủ Doãn, on 24 February by a small column from Hưng Hóa under the command of Lieutenant-Colonel de Maussion, found the route to Tuyên Quang blocked by a strong Chinese defensive position at Hòa Mộc.

Meanwhile, the French government was pressuring Brière de l'Isle to send the 2nd Brigade across the border into Guangxi province, in the hope that a threat to Chinese territory would force China to sue for peace.

On 23 March, in the Battle of Phu Lam Tao, a force of Chinese regulars and Black Flags surprised and routed a French zouave battalion that had been ordered to scout positions around Hưng Hóa in preparation for Giovanninelli's projected offensive against the Yunnan Army.

Future French operations were cancelled on the news of Herbinger's retreat from Lạng Sơn on 28 March, and Courbet was on the point of evacuating Keelung to reinforce the Tonkin expeditionary corps, leaving only a minimum garrison at Makung in the Pescadores, when hostilities were ended in April by the conclusion of preliminaries of peace.

"[80] In 1893 "The Medical World, Volume 11" said "Captain Hugot, of the Zouaves, was inclose pursuit of the infamous Thuyết, one of the most redoubtable, ferocious, and cunning of the Black Flag (Annamite pirates) leaders, the man who prepared and executed the ambuscade at Hue.

[81] The 1892 "The Imperial and Asiatic Quarterly Review and Oriental and Colonial Record" said "The French port of Yến Long was surprised by Chinese and Annamite pirates and the troops driven out with loss.

[85] In order to court the Japanese government, France offered to support Japan's pleas for revision of the unequal treaties of the Bakumatsu era, which provided extra-territoriality and advantageous tariffs to foreigners.

They were obliged to evacuate Formosa and the Pescadores Islands[16] (which Courbet had wanted to retain as a French counterweight to British Hong Kong), but the Chinese withdrawal from Tonkin left the way clear for them to reoccupy Lạng Sơn and to advance up the Red River to Lào Cai on the Yunnan–Tonkin border.

The war had already destroyed Ferry's career, and his successor Henri Brisson also resigned in the wake of the acrimonious 'Tonkin Debate' of December 1885, in which Clemenceau and other opponents of colonial expansion nearly succeeded in securing a French withdrawal from Tonkin.

[16] Fighting ended on 4 April 1885 as a result of peace negotiations due to the Qing court's concerns about the economy, French naval supremacy, lack of foreign support, and northern threats posed by Russia and Japan.