Retreat from Lạng Sơn

The Retreat from Lang Son (French: retraite de Lang-Son) was a controversial French strategic withdrawal in Tonkin at the end of March 1885 that brought down the government of the French premier Jules Ferry and brought the Sino-French War (August 1884 to April 1885) to an end in circumstances of considerable embarrassment for France.

By the middle of March 1885 the military situation in Tonkin had reached a temporary stalemate. In February 1885, in the Lang Son Campaign, the French had captured Lang Son and driven China's Guangxi Army out of Tonkin. In the second half of February General Louis Brière de l'Isle, the general-in-chief of the Tonkin Expeditionary Corps, returned to Hanoi with Lieutenant-Colonel Laurent Giovaninelli's 1st Brigade to relieve the Siege of Tuyen Quang, leaving General François de Négrier at Lang Son with the 2nd Brigade.

Giovanninelli's 1st Brigade faced Tang Jingsong's Yunnan Army around Hung Hoa and Tuyen Quang, while de Négrier's 2nd Brigade at Lang Son faced Pan Dingxin's Guangxi Army. Neither Chinese army had any realistic prospect of launching an offensive for several weeks, while the two French brigades that had jointly captured Lang Son in February were not strong enough to inflict a decisive defeat on either Chinese army separately. 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. Brière de l'Isle and de Négrier examined the possibility of a campaign to capture the major Chinese military depot at Longzhou, 60 kilometres beyond the border, but on 17 March Brière de l'Isle advised the army ministry in Paris that such an operation was beyond his strength. Substantial French reinforcements reached Tonkin in the middle of March, giving Brière de l'Isle a brief opportunity to break the stalemate. He moved the bulk of the reinforcements to Hung Hoa to reinforce the 1st Brigade, intending to attack the Yunnan Army and drive it back beyond Yen Bay. While he and Giovanninelli drew up plans for a western offensive, he ordered de Négrier to hold his positions at Lang Son.

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