The town was occupied by the French in 1885 when it was a very prosperous town.
The French converted it into a military base considered as important to their other base in Cao Bằng.
In 1906, archaeologist Henri Mansuy discovered the Tham Kanh cave near Pho Binh Gia which he named the Ho Binh Gia.
He unearthed unique stone implements and human remains.
In 1922–25 M. Coloni extensively explored Lạng Sơn Province and identified 43 sites related to the ancient Bac Son culture in the mountains.

During the Second World War, even though the Japanese had signed an agreement with Vichy Indo China, they soon reneged on the Agreement, without waiting for the ink to dry on the accord, and launched an offensive on Vietnam by withdrawing their troops from China.
They crossed the Vietnam China border and entered 12 kilometres (7.5 mi) inside, very close to the Lạng Sơn railway station.
The Japanese attacked on 22 September 1940 and by the 25th they captured Lạng Sơn.
However, Vichy had lodged a protest with Emperor Hirohito for the breach of the agreement signed between the two countries, which resulted in a ceasefire to the hostilities by the evening of 26 September, and soon Lạng Sơn was reoccupied by the Vichy forces.

After Ho Chi Minh's government was established in September 1945, Japanese had surrendered to the British and Indian Army, under the terms of the Potsdam Conference, to the south of the 16th parallel, while the Chinese Nationalist Party (the Kuomintang).
As strategy, Ho Chi Minh entered into an agreement with the French so that he could face any threat from the Chinese and a Franco-Vietnamese agreement was signed.
This provided for a free Vietnam within the French Union and the Indochinese federation.
However, the French launched an offensive against the Viet Minh in October 1947 with Lạng Sơn as a their base.
However, the Viet Minh managed to thwart the French Offensive and forced the French to withdraw to Lạng Sơn.
However, the Viet Minh pursue the French Army, they had a very decisive victory on Highway 4 and they had to finally withdraw from Lạng Sơn.
This marked the beginning of First Indochina War
In 1950 the Viet Minh took control of the province and the town.
During February 1979, the Chinese invaded Vietnam through the border town of Don Dong (18 kilometres (11 mi) to the north of Long Son town).
In this war, which lasted for five days, 600,000 soldiers had descended on Vietnam; Lạng Sơn town was the major town that received the major thrust of 200,000 soldiers from China and occupied the capital city of the Northern Province.
However, the Vietnamese had the last say as the Vietnamese army was successful in defeating the Chinese army, which bid a hasty retreat.
This has achieved the status of a folk lore in the province.
The frontier village, which became famous during the war with China, has remnants of the war on display to the visitors.
However the border has been rebuilt and brisk trade flourishes between Vietnam and China through this town.

During the Chinese invasion in 1959 the Lan Son town was also severely damaged, however it has been rebuilt since then.
The old part of the town, near the Kyu Kung River has some interesting historical sites.

On June 7, 1949, the district of Lộc Bình was transferred from Hải Ninh Province into Lạng Sơn.
During the First Indochina War, Lạng Sơn was a part of Liên khu Việt Bắc.
In 1950 the province had 10 districts: Bằng Mạc, Bắc Sơn, Bình Gia, Cao Lộc, Điềm He, Lộc Bình, Ôn Châu, Thoát Lãng, Tràng Định and Văn Uyên.
On July 1, 1956, the district of Hữu Lũng of Bắc Giang Province was transferred into Lạng Sơn, which was placed in the Khu tự trị Việt Bắc (Region of Northern Vietnam), which was formed the same day.
The RNV lasted until December 27, 1975.
In 1963 agricultural cooperativization began between the nationalities of the province.
On December 16, 1964, the district of Điềm He and six communes of Bằng Mạc were merged to form the new district of Văn Quan; at the same time, the district of Ôn Châu and eight communes of Bằng Mạc district came together to form the new
The town was occupied by the French in 1885 when it was a very prosperous town. The French converted it into a military base considered as important to their other base in Cao Bằng. In 1906, archaeologist Henri Mansuy discovered the Tham Kanh cave near Pho Binh Gia which he named the Ho Binh Gia. He unearthed unique stone implements and human remains. In 1922–25 M. Coloni extensively explored Lạng Sơn Province and identified 43 sites related to the ancient Bac Son culture in the mountains.
During the Second World War, even though the Japanese had signed an agreement with Vichy Indo China, they soon reneged on the Agreement, without waiting for the ink to dry on the accord, and launched an offensive on Vietnam by withdrawing their troops from China. They crossed the Vietnam China border and entered 12 kilometres (7.5 mi) inside, very close to the Lạng Sơn railway station. The Japanese attacked on 22 September 1940 and by the 25th they captured Lạng Sơn. However, Vichy had lodged a protest with Emperor Hirohito for the breach of the agreement signed between the two countries, which resulted in a ceasefire to the hostilities by the evening of 26 September, and soon Lạng Sơn was reoccupied by the Vichy forces.
After Ho Chi Minh's government was established in September 1945, Japanese had surrendered to the British and Indian Army, under the terms of the Potsdam Conference, to the south of the 16th parallel, while the Chinese Nationalist Party (the Kuomintang). As strategy, Ho Chi Minh entered into an agreement with the French so that he could face any threat from the Chinese and a Franco-Vietnamese agreement was signed. This provided for a free Vietnam within the French Union and the Indochinese federation. However, the French launched an offensive against the Viet Minh in October 1947 with Lạng Sơn as a their base. However, the Viet Minh managed to thwart the French Offensive and forced the French to withdraw to Lạng Sơn. However, the Viet Minh pursue the French Army, they had a very decisive victory on Highway 4 and they had to finally withdraw from Lạng Sơn. This marked the beginning of First Indochina War
In 1950 the Viet Minh took control of the province and the town. During February 1979, the Chinese invaded Vietnam through the border town of Don Dong (18 kilometres (11 mi) to the north of Long Son town). In this war, which lasted for five days, 600,000 soldiers had descended on Vietnam; Lạng Sơn town was the major town that received the major thrust of 200,000 soldiers from China and occupied the capital city of the Northern Province. However, the Vietnamese had the last say as the Vietnamese army was successful in defeating the Chinese army, which bid a hasty retreat. This has achieved the status of a folk lore in the province. The frontier village, which became famous during the war with China, has remnants of the war on display to the visitors. However the border has been rebuilt and brisk trade flourishes between Vietnam and China through this town.
During the Chinese invasion in 1959 the Lan Son town was also severely damaged, however it has been rebuilt since then. The old part of the town, near the Kyu Kung River has some interesting historical sites.
On June 7, 1949, the district of Lộc Bình was transferred from Hải Ninh Province into Lạng Sơn. During the First Indochina War, Lạng Sơn was a part of Liên khu Việt Bắc. In 1950 the province had 10 districts: Bằng Mạc, Bắc Sơn, Bình Gia, Cao Lộc, Điềm He, Lộc Bình, Ôn Châu, Thoát Lãng, Tràng Định and Văn Uyên. On July 1, 1956, the district of Hữu Lũng of Bắc Giang Province was transferred into Lạng Sơn, which was placed in the Khu tự trị Việt Bắc (Region of Northern Vietnam), which was formed the same day. The RNV lasted until December 27, 1975. In 1963 agricultural cooperativization began between the nationalities of the province. On December 16, 1964, the district of Điềm He and six communes of Bằng Mạc were merged to form the new district of Văn Quan; at the same time, the district of Ôn Châu and eight communes of Bằng Mạc district came together to form the new
Lạng Sơn Province