After the end of the Japanese occupation (1941–1945) and the expulsion from Saigon of the Communist-led, nationalist Viet Minh in 1946, the territory was reorganized as the Autonomous Republic of Cochinchina by the French, a controversial decision that helped trigger the First Indochina War.

In 1867, French Admiral Pierre de la Grandière forced the Vietnamese to surrender three additional provinces, Châu Đốc, Hà Tiên and Vĩnh Long.

[2] The French began rubber production in Cochinchina in 1907, seeking a share of the monopoly profits that the British were earning from their plantations in Malaya.

[12] As they expanded in response to the increased rubber demand after the First World War, the European plantations recruited, as indentured labour, workers from "the overcrowded villages of the Red River Delta in Tonkin and the coastal lowlands of Annam".

[22] In April of that year, the Communist Party and their Trotskyist left opposition ran a common slate for the municipal elections, with both their respective leaders Nguyễn Văn Tạo and Tạ Thu Thâu winning seats.

The exceptional anti-colonial unity of the left, however, was split by the lengthening shadow of the Moscow Trials and growing protest over the failure of the Communist-supported Popular Front to deliver constitutional reform.

[23] Colonial Minister Marius Moutet, a socialist, commented that he had sought "a wide consultation with all elements of the popular [will]," but with "Trotskyist-Communists intervening in the villages to menace and intimidate the peasant section of the population, taking all authority from the public officials," the necessary "formula" had not been found.

[24] In the April 1939 Cochinchina Council elections, Tạ Thu Thâu led a "Workers' and Peasants' Slate" into victory over both the moderate Constitutionalists and the Communists' Democratic Front.

Key to their success was popular opposition to the war taxes ("national defence levy") that the Communist Party, in the spirit of the Franco-Soviet accord, had felt obliged to support.

[25] Brévié set the election results aside and wrote to Colonial Minister Georges Mandel: "the Trotskyists under the leadership of Ta Thu Thau want to take advantage of a possible war in order to win total liberation."

Under the slogan "Land to the tillers, freedom for the workers and independence for Vietnam",[27] the Communist Party in Cochinchina instigated a widespread insurrection in November 1940.

On 9 December 1940, an agreement was reached with the Vichy government whereby French sovereignty over its army and administrative affairs was confirmed, but Japanese forces were free to fight the war against the Allies from Indochinese soil.

With the Soviets tied down, the high command concluded that a "strike south" would solve the problems posed for Japan by the American-led oil embargo.

To prepare for an invasion of the oil-rich Dutch East Indies, some 140,000 Japanese troops occupied southern French Indochina on 28 July 1941.

"[33] In August 1945, as they faced defeat, the Japanese belatedly created a puppet state, incorporating Cochinchina in the Empire of Vietnam under the nominal authority of the Bảo Đại.

When, for the declared purpose of disarming the Japanese, the Viet Minh accommodated the landing and strategic positioning of their wartime "democratic allies", the British, rival political groups turned out in force, including the syncretic Hoa Hao and Cao Dai sects.

On 7 and 8 September 1945, in the delta city of Cần Thơ, the committee had to rely on the Jeunesse d'Avant-Garde / Thanh Niên Tiền Phong (Vanguard Youth), who had contributed to civil defence and policing under Japanese.

[39][40] On 1 June 1946, while the Viet Minh leadership was in France for negotiations, at the initiative of High Commissioner d'Argenlieu and in violation of the 6 March Ho–Sainteny agreement, a local territorial assembly proclaimed an "Autonomous Republic".

[42] The next year, the Provisional Central Government of Vietnam was proclaimed with the merger of Annam and Tonkin: Xuân became its Prime minister and left office in Cochinchina, where he was replaced by Trần Văn Hữu.