France's Indochina war ran from Saigon 1945 to Dien Bien Phu's shadow
The First Indochina War matched the French Union against the Viet Minh from 19 December 1946 into 1954. Potsdam split the peninsula at 16°N; France seized Saigon in September 1945, China and the Soviets recognized the DRV in 1950, and remote-base battles like Na San previewed a wider Cold War fight.
France swallowed Vietnam piece by piece between 1858 and 1887. An early resistance figure, Phan Boi Chau, looked to modernised Japan for help, was expelled at French insistence, founded a movement in Guangzhou after China's 1911 revolution, and was seized by French agents in Shanghai in 1925. In September 1940 Japan invaded Indochina but left the Vichy French administration in place, which nationalists saw as a puppet regime twice over. Ho Chi Minh founded the Viet Minh in 1941 as a broad front stressing national liberation over class struggle.
In March 1945 Japan ousted the French and installed Emperor Bao Dai over a nominally independent Vietnam. The wartime famine of 1944 and 1945 killed one to two million people in the Red River Delta, and Japanese destruction was valued at two billion dollars. Roosevelt privately opposed a French return, even suggesting Chinese control, but that resistance faded after his death. Following Japan's surrender, Bao Dai abdicated on 25 August, and on 2 September Ho proclaimed independence, quoting the American Declaration's words on equality.
Potsdam planners had placed Indochina south of the 16th parallel under Mountbatten's command, and on 23 September French troops toppled the Viet Minh administration in Saigon, sparking immediate guerrilla fighting. Full war erupted on 19 December 1946. Mao's victory in 1949 transformed the conflict: in 1950 Beijing and Moscow recognised Ho's republic while Washington recognised the State of Vietnam, and fighting grew increasingly conventional. France's tactic of luring the Viet Minh into assaulting fortified remote bases worked at Na San, but tanks were of little use in forest, air power was thin, and many soldiers came from the colonies.
Somewhere between 400,000 and about 843,000 soldiers died, along with 125,000 to 400,000 civilians, and both sides committed atrocities, including the massacre by French troops at My Trach. The State of Vietnam won legal independence in June 1954, and although the Viet Minh held most of the country, Chinese pressure made them accept partition at the 17th parallel at the Geneva Conference that July; fighting formally ended on 11 August 1954.
Source: First Indochina War
