During World War II, after the fall of France and establishment of Vichy France, the French had lost practical control in French Indochina to the Japanese, but Japan stayed in the background while giving the Vichy French administrators nominal control. This changed on 9 March 1945 when Japan officially took over. To gain the support of the Vietnamese people, Imperial Japan declared it would return sovereignty to Vietnam. Emperor Bảo Đại declared the Treaty of Huế (1884) made with France in 1884 void. Trần Trọng Kim, a renowned historian and scholar, was chosen to lead the government as prime minister.
Kim and his ministers spent a substantial amount of time on constitutional matters at their first meeting in Huế on 4 May 1945. One of their first resolutions was to alter the national name to Việt Nam. This was seen as a significant and urgent task. It implied territorial unity; "Việt Nam" had been Emperor Gia Long's choice for the name of the country since he unified the modern territory of Việt Nam in 1802. Furthermore, this was the first time that Vietnamese nationalists in the northern, central and southern regions of the country officially recognized this name. In March, activists in the North always mentioned Đại Việt (Great Việt), the name used before the 15th century by the Lê Dynasty and its predecessors, while those in the South used Vietnam, and the central leaders used An Nam (Peaceful South) or Đại Nam (Great South, which was used by the Nguyễn Lords).
Kim also renamed the three regions of the country — the northern (former Tonkin or Bắc Kỳ) became Bắc Bộ, the central region (former Annam or Trung Kỳ) became Trung Bộ, and the southern areas (former Cochinchina or Nam Kỳ) became Nam Bộ. Kim did this even though at the time the Japanese had only given him direct authority over the northern and central regions of Vietnam. When France had finished its conquest of Vietnam in 1885, only southern Vietnam was made a direct colony under the name of Cochinchina. The northern and central regions were designated as protectorates as Tonkin and Annam. When the Empire of Vietnam was proclaimed, the Japanese retained direct control of Cochinchina, in the same way as their French predecessors.
Thuận Hóa, the pre-colonial name for Huế, was restored. Kim's officials worked to find a French substitute for the word "Annamite", which was used to denote Vietnamese people and their characteristics as described in French literature and official use. "Annamite" was considered derogatory, and it was replaced with "Vietnamien" (Vietnamese). Apart from Thuận Hóa, these terms have been internationally accepted since Kim ordered the changes. Given that the French colonial authorities emphatically distinguished the three regions of "Tonkin", "Annam", and "Cochinchina" as separate entities, implying a lack of national culture or political integration, Kim's first acts were seen as symbolic and the end of generations of frustration among Vietnamese intelligentsia and revolutionaries.
On 12 June 1945, Kim selected a new national flag — a yellow, rectangular banner with three horizontal red stripes modeled after the Li Kwai in the Book of Changes — and a new national anthem, the old hymn Dang Dan Cung (The King Mounts His Throne). This decision ended three months of speculation concerning a new flag for Vietnam.
Kim's government strongly emphasised educational reform, focusing on the development of technical training, particularly the use of romanised script (quốc ngữ) as the primary language of instruction. After less than two months in power, Kim organized the first primary examinations in Vietnamese, the language he intended to use in the advanced tests. Education minister Hoang Xuan Han strove to Vietnamise public secondary education. His reforms took more than four months to achieve their results, and have been regarded as a stepping stone for the successor Viet Minh government's launch of compulsory mass education. In July, when the Japanese decided to grant Vietnam full independence and territorial unification, Kim's government was about to begin a new round of reform, by naming a committee to create a new national education system.
The Justice minister Trịnh Đình Thảo launched an attempt at judicial reform. In May 1945, he created the Committee for the Reform and Unification of Laws in Huế, which he headed. His ministry reevaluated the sentences of political prisoners, releasing a number of anti-French activists and restoring the civil rights of others. This led to the release of a number of Communist cadres who returned to their former cells, and actively participated in the destruction of Kim's government.
One of the most notable changes implemented by Kim's government was the encouragement of mass political participation. In memorial ceremonies, Kim honoured all national heroes, ranging from the legendary national founders, the Hùng kings to slain anti-French revolutionaries such as Nguyễn Thái Học, the leader of the Vietnamese Nationalist Party (Việt Nam Quốc Dân Đảng) who was executed with twelve comrades in 1930 in the aftermath of the Yên Bái mutiny.
A committee was organised to select a list of national heroes for induction into the Temple of Martyrs (Nghia Liet Tu). City streets were renamed. In Huế, Jules Ferry was replaced on the signboards of a main thoroughfare by Lê Lợi, the founder of the Lê Dynasty who expelled the Chinese in 1427. General Trần Hưng Đạo, who twice repelled Mongol invasions in the 13th century, replaced Paul Bert. On August 1, the new mayor of Hanoi, Tran Van Lai, ordered the demolition of French built statues in the city parks in his campaign to Wipe Out Humiliating Remnants. Similar campaigns were enacted in southern Vietnam in late August. Meanwhile, the freedom of the press was instituted, resulting in the publication of the pieces of anti-French movements and critical essays on French collaborators. Heavy criticism was even extended to Nguyen Huu Do, the great grandfather of Bảo Đại who was notable in assisting the French conquest of Dai Nam in the 1880s.
Kim put particular emphasis on the mobilisation of youth. Youth Minister Phan Anh, attempted to centralise and heavily regulate all youth organizations, which had proliferated immediately after the Japanese coup. On May 25, an imperial order decreed an inclusive, hierarchical structure for youth organizations. At the apex was the National Youth Council, a consultative body, which advised the minister. Similar councils were to be organised down to the district level. Meanwhile, young people were asked to join the local squads or groups, from provincial to communal levels. They were given physical training and were charged with maintaining security in their communes. Each provincial town had a training centre, where month-long paramilitary courses were on offer.
The government also established a national center for the Advanced Front Youth (Thanh nien tien tuyen) in Huế. It was inaugurated on June 2, with the intention of being the centrepiece for future officer training. In late July, regional social youth centers were established in Hanoi, Huế, and Saigon. In Hanoi, the General Association of Students and Youth (Tong Hoi Sinh vien va Thanh Nien) was animated by the fervor of independence. The City University in Hanoi became a focal point of political agitation. By May and June, there was evidence that communist Cadres of the Viet Minh front, had infiltrated the university's youth and famine relief associations. In the face of the rising Viet Minh front, the Japanese attempted to contact its leaders, but their messengers were killed by the Viet Minh. The Kempeitai retaliated, arresting hundreds of pro-communist Vietnamese youths in late June.
The most notable achievement of Kim's Empire of Vietnam was the successful negotiation with Japan for the territorial unification of the nation. The French had subdivided Vietnam into three separate regions: Cochinchina (in 1862) and Annam and Tonkin (both in 1884). Cochinchina was placed under direct rule while the latter two were officially designated as protectorates. Immediately after the coup which terminated French rule, the Japanese authorities were not enthusiastic about the territorial unification of Vietnam. However, after the formation of Kim's cabinet in April, Japan quickly agreed to return what was then Tonkin and Annam to Kim's authority, although it retained control of the cities of Hanoi, Haiphong, and Da Nang. Meanwhile, southern Vietnam remained under direct Japanese control, just as Cochinchina had been under French rule.
Beginning in May 1945, Foreign Minister Tran Van Chuong entered into negotiations with the Japanese in Hanoi for the return of the three cities to Vietnamese rule, but the Japanese stalled because Hanoi and Haiphong were seen as strategic points in their war defence. It was only in June and July that the Japanese allowed the process of national unification to take place. On June 16, Bảo Đại issued a decree proclaiming the impending reunification of Vietnam. On June 29, General Yuitsu Tsuchihashi signed a series of decrees transferring some of the duties of the government general-including customs, information, youth and sports- to the governments of Vietnam, Laos and Cambodia, effective July 1. This was followed by Bảo Đại's issuing of four imperial orders: establishment of the National Consultative Committee (Hoi dong Tu van Quoc Gia); a committee of fifteen to work on the creation of a constitution; a fifteen-member committee to examine administrative reform, legislation, and finance; and a committee for educational reform. For the first time, leaders from southern regions were invited to join these committees.
Other developments in southern Vietnam in early July were seen as preparatory Japanese steps towards granting territorial reunification to Vietnam. In early July, when southern Vietnam was abuzz with the spirit of independence and mass political participation due to the creation of the Vanguard Youth organizations in Saigon and other regional centres, Governor Minoda announced the organisation of the Hoi Nghi Nam (Council of Nam Bo) to facilitate his governance. This council was charged with advising the Japanese based on questions submitted to it by the Japanese and for overseeing provincial affairs. Minoda underlined that its primary aim was to make the Vietnamese population believe that they had to closely collaborate with the Japanese, because "if the Japanese lose the war, the independence of Indochina would not become complete." At its inauguration of the Council of Nam Bo on July 21, Minoda implicitly referred to the unification of Vietnam. Tran Van An was appointed as the president of the Council, and Kha Vang Can, a leader of the Vanguard Youth, was appointed to be his deputy.
On July 13, Kim arrived in Hanoi to directly conduct negotiations with Governor-General Tsuchihashi. Tsuchihashi assented to return control of Hanoi, Haiphong, and Da Nang to Kim's government, taking effect on July 20. After protracted negotiation, it was also agreed that Nam Bo was to be reintegrated into Vietnam and that Kim would journey to Saigon to attend the reunification ceremonies on August 8.
Kim's historic achievement was immediately overshadowed by external pressure and domestic infighting. On July 26, the leaders of the Allies issued a declaration demanding the unconditional surrender of Japan. Japan was on the defensive and quickly losing ground, and its aim was no longer to win the war, but simply to find an honorable ceasefire. On the Vietnamese front, the possibility of future punishment by the Allied forces for collaboration with the Japanese discouraged many possible supporters of Kim. His ministers and public servant corps began to dwindle in number. The Imperial Commissioner of Bac Bo, Phan Ke Toai, accompanied by his son and other Viet Minh sympathisers and secret communists such as Nguyen Manh Ha and Hoàng Minh Giám, submitted his resignation. Nguyen Xuan Chu, a leader of the Vietnamese Patriotic Party (Viet-Nam Ai Quoc Dang) and one of the five members of Cường Để's National Reconstruction Committee, refused the offer of replacing Toai. Returning to Thuận Hóa, Kim arrived to find increasing conflict among his ministers. Chuong wanted credit for arranging the integration of the three ceded cities and southern Vietnam to Kim's government and was regarded as having Prime Ministerial designs himself. The government meetings of August 5 and 6 were headlined by personal disputes and the resignation of the ministers of interior, economy, and supplies. Ho Ta Khanh, the economic minister, went further and demanded the resignation of the government. Khanh proposed that the Viet Minh be given a chance to govern because of its strength. The government resigned on August 7. Bảo Đại asked Kim to form a new government, but the end of the war made this impossible.
On August 8, 1945, the Soviet Union declared war on Japan and invaded Manchuria. The following day, a second atomic bomb was dropped on Nagasaki, and Japan's resistance to the Allies was quickly ended. Japan decided to give Kim and Vietnamese nationalists the full independence and territorial unification that they had sought for decades. Kim was urged many times to come to Saigon to officially accept control of Nam Bo. Multiple factors prevented Kim from leaving the capital. From August 8 onward, Pham Khac Hoe, Bảo Đại's office director, was instructed by Ton Quang Phiet (the future chairman of the Viet Minh's Revolutionary Committee in Huế) to persuade the Emperor to abdicate voluntarily.
In order to carry out his mission, Hoe persistently disrupted Kim's activities, particularly by citing Kim's failure to call the most influential figures to Thuận Hóa to form a new government. Meanwhile, Interior Minister Nam, cited the communist uprisings in Thanh Hóa and Quảng Ngãi in central Vietnam to discourage Kim from traveling to Saigon. The acceptance of the handover of Nam Bo was thus temporarily placed at the feet of the Council of Nam Bo.
On August 14, Bảo Đại appointed Nguyen Van Sam, former president of the Journalists' Syndicate, to the post of Imperial Commissioner of Nam Bo. Sam left Thuận Hóa for Saigon. However, he was delayed en route as the Viet Minh had taken advantage of the military power vacuum caused by the Japanese surrender to launch a general insurrection with the aim of seizing control of the country.
In August, Vietnam went through a period regarded as one of its most eventful phases, amidst the backdrop of rapid change in global politics. On the one hand, the Allies began to put into effect their postwar plans for Vietnam, which included the disarmament of Japanese troops and the division of Vietnam into spheres of influence. The Japanese military and civilian personnel in Vietnam were hamstrung by the unconditional surrender of their government and the possibility of Allied retribution. With respect to the Vietnamese, the Japanese were split psychologically and ideologically. Some Japanese favoured the Viet Minh, releasing Communist political prisoners, arming the Viet Minh front, and even volunteering their services. Others, including senior military officers, wanted to use their forces to support Kim's government and to crush the communists. Amid the political confusion and power vacuum engulfing the country, a race to power by diverse Vietnamese political groups took place.
On the eve of Japan's surrender, Kim and his supporters tried to take control of the situation. On August 12, Kim's outgoing government was retained as "Provisional Government" to oversee the day-to-day running of the country. Kim asked Bảo Đại to issue an imperial order on August 14 repealing the treaties of 1862 and 1874, thus removing the last French claims to sovereign rights over Vietnam. Messengers were sent from the central capital to northern and southern Vietnam to reunify diverse groups under the central government in Thuận Hóa, but they were apprehended en route by the Viet Minh.
Even though Bảo Đại's messengers were cut off, non-communist leaders in northern and southern Vietnam attempted to challenge the Viet Minh. In Bac Bo, Nguyen Xuan Chu obtained Kim's approval to form the Committee for National Salvation, and he was appointed by Kim as chairman of the Political Directorate of Bac Bo. In Nam Bo, on August 17, it was announced that all non-Viet Minh factions, including Trotskyites and the southern religious sects of Cao Đài and Hòa Hảo, had joined forces to create the Mặt trận Quốc gia Thống nhất (National Unified Front). Trần Quang Vinh, the Cao Đài leader, and Huỳnh Phú Sổ, the founder of the Hòa Hảo, also issued a communique proclaiming an alliance. On August 19 in Saigon, the Vanguard Youth organised their second official oath-taking ceremony, vowing to defend Vietnamese independence at all costs. The next day, Ho Van Nga assumed the interim office of Imperial Commissioner and appointed Kha Vang Can, the Vanguard Youth leader, commander of Saigon and Cholon. Nguyen Van Sam's arrival in Saigon on August 22 provided the National Unified Front with the official declaration of national independence and territorial reunification.
Nevertheless, the Viet Minh prevailed in the power struggle with their August Revolution. On August 17, Viet Minh cadres in Hanoi took control of a mass demonstration organised by the General Association of Civil Servants. The rally was originally aimed at celebrating independence and territorial reunification and supporting Kim's government. Two days later, Nguyen Xuan Chu was forced to hand over authority to the Viet Minh. Combined with the official cease-fire of the Japanese army on August 21, this threw Kim's government into disarray and it collapsed. On August 23, the Viet Minh seized power in Huế. Two days later, Bảo Đại officially abdicated, and Nguyen Van Sam handed over power to the Viet Minh in Saigon. The Empire of Viet-Nam had fallen along with Japan's Greater East Asia Co-Prosperity Sphere.