Cochinchina (/ˈkoʊtʃɪnˌtʃaɪnə/; Vietnamese: Nam Kỳ; Khmer: កូសាំងស៊ីន, Kausangsin; French: Cochinchine) is a region encompassing the southern third of current Vietnam whose principal city is Saigon or Prey Nokor in Khmer. It was a French colony from 1862 to 1954. The later state of South Vietnam was created in 1954 by combining Cochinchina with southern Annam. In Vietnamese, the region is called Nam Bộ. Historically, it was Gia Định (1779–1832), Nam Kỳ (1834–1945), Nam Bộ (1945–48), Nam phần (1948–56), Nam Việt (1956–75), and later Miền Nam. In French, it was called la colonie de Cochinchine.
In the 17th century, Vietnam was divided between the Trịnh lords to the north and the Nguyễn lords to the south. The northern section was called Tonkin by Europeans, and the southern part called Cochinchina by most Europeans and Quinam by the Dutch. Cochinchina was never a single united administrative unit until the French seized it in the 1850s.
During the French colonial period, the label moved further south, and came to refer exclusively to the southernmost part of Vietnam, controlled by Cambodia in prior centuries, and lying to its southeast. The capital of the French colony of Cochinchina was at Saigon. The two other parts of Vietnam at the time were known as Annam (Central Vietnam) and Tonkin (Northern Vietnam).
The conquest of the south of present-day Vietnam was a long process of territorial acquisition by the Vietnamese. It is called Nam tiến (Chinese characters: 南進, English meaning "South[ern] Advance") by Vietnamese historians. Vietnam (then known as Đại Việt) nearly doubled its territory in 1470 under the great king Lê Thánh Tông, at the expense of Champa. The next two hundred years was a time of territorial consolidation and civil war with only gradual expansion south.
In 1516, Portuguese traders sailing from Malacca landed in Da Nang, Champa, and established a presence there. They named the area "Cochin-China", borrowing the first part from the Malay Kuchi, which referred to all of Vietnam, and which in turn derived from the Chinese Jiāozhǐ, pronounced Giao Chỉ in Vietnam. They appended the "China" specifier to distinguish the area from the city and the princely state of Cochin in India, their first headquarters in the Malabar Coast,
As a result of a civil war that started in 1520, the Emperor of China sent a commission to study the political status of Annam in 1536. As a consequence of the delivered report, he declared war against the Mạc dynasty. The nominal ruler of the Mạc died at the very time that the Chinese armies passed the frontiers of the kingdom in 1537, and his father, Mạc Đăng Dung (the real power in any case), hurried to submit to the Imperial will, and declared himself to be a vassal of China. The Chinese declared that both the Lê dynasty and the Mạc had a right to part of the lands and so they recognised the Lê rule in the southern part of Vietnam while at the same time recognising the Mạc rule in the northern part, which was called Tunquin (i.e. Tonkin). This was to be a feudatory state of China under the government of the Mạc.
However, this arrangement did not last long. In 1592, Trịnh Tùng, leading the Royal (Trịnh) army, conquered nearly all of the Mạc territory and moved the Lê kings back to the original capital of Hanoi. The Mạc only held on to a tiny part of north Vietnam until 1667, when Trịnh Tạc conquered the last Mạc lands.
In 1623, Nguyễn Phúc Nguyên, the lord of the (then) southern provinces of Vietnam, established a trading community at Saigon, then called Prey Nakor, with the consent of the king of Cambodia, Chey Chettha II. Over the next 50 years, Vietnamese control slowly expanded in this area but only gradually as the Nguyễn were fighting a protracted civil war with the Trịnh lords in the north.
With the end of the war with the Trịnh, the Nguyễn were able to devote more effort (and military force) to conquest of the south. First, the remaining Champa territories were taken; next, the areas around the Mekong river were placed under Vietnamese control.
At least three wars were fought between the Nguyễn lords and the Cambodian kings in the period 1715 to 1770 with the Vietnamese gaining more territory with each war. The wars all involved the much more powerful Siamese kings who fought on behalf of their vassals, the Cambodians. In the late 18th century, Vietnam was briefly unified under the Tây Sơn. These were three brothers, former peasants, who succeeded in conquering first the lands of the Nguyễn and then the lands of the Trịnh.
Final unification came under Nguyễn Phúc Ánh, a remarkably tenacious member of the Nguyễn noble family who fought for 25 years against the Tây Sơn and ultimately conquered the entire country in 1802. He ruled all of Vietnam under the name Gia Long. His son Minh Mạng reigned from 14 February 1820 until 20 January 1841 what was known to the British as Cochin China and to the Americans as hyphenated Cochin-China. In hopes of negotiating commercial treaties, the British in 1822 sent East India Company agent John Crawfurd, and the Americans in 1833 sent diplomatist Edmund Roberts, who returned in 1836. Neither envoy was fully cognizant of conditions within the country, and neither succeeded.
Gia Long's successors (see the Nguyễn dynasty for details) repelled the Siamese from Cambodia and even annexed Phnom Penh and surrounding territory in the war of 1831 to 1834, but were forced to relinquish these conquests in the war of 1841 to 1845.
In 1858, the French government of Napoleon III, with the help of Spanish troops arriving from the Philippines (which was a Spanish colony at the time), decided to take over the southern part of Vietnam ; the Vietnamese government was forced to cede the provinces Biên Hòa, Gia Định and Định Tường to France in June 1862. These territories, which were then called by the French lower Cochinchina (Basse-Cochinchine) became a colony called Cochinchina.
In 1887, the colony of French Cochinchina became part of the Union of French Indochina, while remaining separated from the protectorates of Annam and Tonkin.
Cochinchina was occupied by Japan during World War II (1941–45), but was restored to France afterwards. After 1945, the status of Cochinchina was a subject of discord between France and Ho Chi Minh's Viet Minh. In 1946, the French proclaimed Cochinchina an "autonomous republic", which was one of the causes of the First Indochina War. In 1948, Cochinchina was renaimed as the Provisional Government of South Vietnam. It was merged the next year with the Provisional Central Government of Vietnam, and the State of Vietnam, with former emperor Bảo Đại as head of state, was then officially established.
After the First Indochina War, the foreign powers allowed the Khmer Krom's land in Cochinchina to be subject to settlement by anti-Communist Vietnamese from northern Vietnam who were fleeing from Ho Chi Minh. Cochinchina was then merged with southern Annam to form the Republic of Vietnam (South Vietnam).