Cao Bằng Province in the context of "Pearl River"

Guangxi, officially the Guangxi Zhuang Autonomous Region, is an autonomous region of the People's Republic of China, located in South China and bordering Vietnam (Tuyên Quang, Cao Bằng, Lạng Sơn, and Quảng Ninh Provinces) and the Gulf of Tonkin. Formerly a province, Guangxi became an autonomous region in 1958. Its current capital is Nanning.

Guangxi's location, in mountainous terrain in the far south of China, has placed it on the frontier of Chinese civilization throughout much of Chinese history. The current name "Guang" means "expanse" and has been associated with the region since the creation of Guang Prefecture in 226 AD. It was given provincial level status during the Yuan dynasty, but even into the 20th century, it was considered an open, wild territory. The abbreviation of the region (Chinese: 桂; Hanyu pinyin: Guì; Zhuang: Gvei) comes from the name of the city of Guilin, the provincial capital during both the Ming and Qing dynasties.

In mid-1940, Nazi Germany rapidly defeated the French Third Republic, and the colonial administration of French Indochina (modern-day Vietnam, Laos and Cambodia) passed to the French State (Vichy France). Many concessions were granted to the Empire of Japan, such as the use of ports, airfields, and railroads. Japanese troops first entered parts of Indochina in September 1940, and by July 1941 Japan had extended its control over the whole of French Indochina. The United States, concerned by Japanese expansion, started putting embargoes on exports of steel and oil to Japan from July 1940. The desire to escape these embargoes and to become self-sufficient in resources ultimately contributed to Japan's decision to attack on December 7, 1941, the British Empire (in Hong Kong and Malaya) and simultaneously the United States (in the Philippines and at Pearl Harbor, Hawaii). This led to the United States declaring war against Japan on December 8, 1941. The United States then joined the side of the British Empire, at war with Germany since 1939, and its existing allies in the fight against the Axis powers.

Indochinese communists had set up a covert headquarters in Cao Bằng Province in 1941, but most of the Vietnamese resistance to Japan, France, or both, including both communist and non-communist groups, remained based over the border, in China. As part of their opposition to Japanese expansion, the Chinese had fostered the formation of a Vietnamese nationalist resistance movement, the Dong Minh Hoi (DMH), in Nanking in 1935/1936; this included communists, but was not controlled by them. This did not provide the desired results, so the Chinese Communist Party sent Ho Chi Minh to Vietnam in 1941 to lead an underground centered on the communist Viet Minh. Ho was the senior Comintern agent in Southeast Asia, and was in China as an advisor to the Chinese communist armed forces. This mission was assisted by European intelligence agencies, and later the US Office of Strategic Services (OSS). Free French intelligence also tried to affect developments in the Vichy-Japanese collaboration.

The Mạc dynasty (Vietnamese: Nhà Mạc/triều Mạc; Hán-Nôm: 茹莫/朝莫) (1527–1677), officially Đại Việt (Chữ Hán: 大越), was a Vietnamese dynasty which ruled over a unified Vietnam between 1527 and 1540, and northern Vietnam from 1540 until 1593. The Mạc dynasty lost control over the capital Đông Kinh (modern Hanoi) for the last time in its wars against the Later Lê dynasty and the Trịnh Lords in 1592. Subsequent members of the Mạc dynasty ruled over the province of Cao Bằng with the direct support of the Chinese Ming and Qing dynasties until 1677 (with members of the Mạc dynasty accepted as officials of the Later Lê dynasty from 1627).

The Yi or Nuosu people (Nuosu: ꆈꌠ, [nɔ̄sū]; see also § Names and subgroups) are an ethnic group in southern China. Numbering nine million people, they are the sixth largest of the 55 ethnic minority groups recognized by the Chinese government. They live primarily in rural areas of Sichuan, Yunnan, Guizhou, and Guangxi, usually in mountainous regions. The Liangshan Yi Autonomous Prefecture is home to the largest population of Yi people within China, with two million Yi people in the region. In neighbouring Vietnam, as of 2019, there are 4,827 Lô Lô people (a subgroup of the Yi) living in the Hà Giang, Cao Bằng, and Lào Cai provinces, in the country's north.

The Yi speak various Loloish languages, closely related to Burmese. The prestige variety is Nuosu, which is written in the Yi script.

The Giáy people (Vietnamese: người Giáy [ŋɯɤi˨˩ zɑi˧˥]), known in Laos as the Nhang or Yang, are an ethnic group in Vietnam and Laos. Most live in the mountainous northern provinces of Lào Cai, Hà Giang, Lai Châu, and Cao Bằng. In 2019 the population was 67,858.

The Tày people, also known as the Thổ, T'o, Tai Tho, Ngan, Phen, Thu Lao, or Pa Di, is a Central Tai-speaking ethnic group who live in northern Vietnam. According to a 2019 census, there are 1.8 million Tày people living in Vietnam. This makes them the second largest ethnic group in Vietnam after the majority Kinh (Vietnamese) ethnic group. Most live in northern Vietnam in the Cao Bằng, Lạng Sơn, Bắc Kạn, Thái Nguyên, and Quảng Ninh provinces, along the valleys and the lower slopes of the mountains. They also live in some regions of the Bắc Ninh and Bắc Giang provinces. They inhabit fertile plains and are generally agriculturalists, mainly cultivating rice. They also cultivate maize, and sweet potato among other things.