The First Indochina War (generally known as the Indochina War in France, and as the Anti-French Resistance War in Vietnam) was fought between France and Việt Minh (Democratic Republic of Vietnam), and their respective allies, from 19 December 1946 until 20 July 1954. Việt Minh was led by Võ Nguyên Giáp and Hồ Chí Minh. Most of the fighting took place in Tonkin in Northern Vietnam, although the conflict engulfed the entire country and also extended into the neighboring French Indochina protectorates of Laos and Cambodia.

At the Potsdam Conference in July 1945, the allied Combined Chiefs of Staff decided that Indochina south of latitude 16° north was to be included in the Southeast Asia Command under British Admiral Mountbatten. On V-J Day, September 2, Hồ Chí Minh proclaimed in Hanoi (Tonkin's capital) the establishment of the Democratic Republic of Vietnam (DRV). In late September 1945, Chinese forces entered Tonkin, and Japanese forces to the north of that line surrendered to Generalissimo Chiang Kai-shek. At the same time, British forces landed in Saigon (Cochinchina's capital), and Japanese forces in the south surrendered to the British. The Chinese accepted the DRV under Hồ Chí Minh, then in power in Hanoi. The British refused to do likewise in Saigon, and deferred to the French, against the ostensible support of the Việt Minh by American OSS representatives. The DRV ruled as the only civil government in all of Vietnam for a period of about 20 days, after the abdication of Emperor Bảo Đại, who had governed under the Japanese rule. On 23 September 1945, with the knowledge of the British commander in Saigon, French forces overthrew the local DRV government, and declared French authority restored in Cochinchina. Guerrilla warfare began around Saigon immediately, but the French gradually retook control of Indochina. Hồ Chí Minh agreed to talk with France but negotiations failed. After one year of low-level conflict, all-out war broke out in December 1946 between French and Việt Minh forces as Hồ Chí Minh and his government went underground. The French tried to stabilize Indochina by reorganizing it as a Federation of Associated States. In 1949, they put former Emperor Bảo Đại back in power, as the ruler of a newly established State of Vietnam.

The first few years of the war involved a low-level rural insurgency against the French. By 1949 the conflict had turned into a conventional war between two armies equipped with modern weapons, with the French supplied by the United States, and the Việt Minh supplied by the Soviet Union and a newly communist China. French Union forces included colonial troops from the empire - North Africans; Laotian, Cambodian and Vietnamese ethnic minorities; Sub-Saharan Africans - and professional French troops, European volunteers, and units of the Foreign Legion. The use of metropolitan recruits was forbidden by the government to prevent the war from becoming more unpopular at home. It was called the "dirty war" (la sale guerre) by leftists in France.

The French strategy of inducing the Việt Minh to attack well-defended bases in remote areas at the end of their logistical trails was validated during the Battle of Nà Sản. French efforts were hampered by the limited usefulness of tanks in a forested environment, the lack of a strong air force, and reliance on soldiers from French colonies. The Việt Minh used novel and efficient tactics, including direct artillery fire, convoy ambushes, and anti-aircraft weaponry to impede land and air resupplies together with a strategy based on recruiting a sizable regular army facilitated by large popular support. They used guerrilla warfare doctrine and instruction developed from China, and used war materiel provided by the Soviet Union. This combination proved fatal for the French bases, culminating in a decisive French defeat at the Battle of Dien Bien Phu.

An estimated 400,000 to 842,707 soldiers died during the war as well as between 125,000 and 400,000 civilians. Both sides committed war crimes during the conflict, including killings of civilians (such as the Mỹ Trạch massacre by French troops), rape and torture. At the International Geneva Conference on July 21, 1954, the new socialist French government and the Việt Minh made an agreement which gave the Việt Minh control of North Vietnam above the 17th parallel, an agreement that was rejected by the State of Vietnam and the United States. A year later, Bảo Đại would be deposed by his prime minister, Ngô Đình Diệm, creating the Republic of Vietnam (South Vietnam). Soon an insurgency, backed by the communist north, developed against Diệm's anti-communist government. This conflict, known as the Vietnam War, included large U.S. military intervention in support of the South Vietnamese and ended in 1975 with the defeat of South Vietnam to the North Vietnamese and the reunification of Vietnam.