First Indochina War

The First Indochina War was fought in French Indochina from December 19, 1946 to August 1, 1954. Other names for the war are the French Indochina War, Anti-French War, Franco-Vietnamese War, Franco-Vietminh War, Indochina War, Dirty War in France, and Anti-French Resistance War in contemporary Vietnam. The war was fought between the French Union's French Far East Expeditionary Corps, led by France and supported by Emperor Bảo Đại's Vietnamese National Army on one side, and the Việt Minh, led by Hồ Chí Minh and Võ Nguyên Giáp on the other. Most of the fighting took place in Tonkin in Northern Vietnam, but the conflict spread over the entire country and also extended into the neighboring French Indochina protectorates of Laos and Cambodia.
Since WWII.
The French reoccupied Indochina after the Second World War after the territory had been part of the Empire of Japan. The Việt Minh launched a rebellion against the French authority. The first few years of the war involved a low-level rural insurgency against French authority. However, after the Chinese communists had reached the Northern border of Vietnam in 1949, the conflict turned into a conventional war between two armies, which had modern weapons supplied by the United States and the Soviet Union.
French Union forces included colonial troops from the whole former empire (Moroccan, Algerian, Tunisian, Laotian, Cambodian, Vietnamese and Vietnamese ethnic minorities), French professional troops and units of the French Foreign Legion. The use of metropolitan recruits was forbidden by the governments to prevent the war from becoming even more unpopular at home. It was called the "dirty war" ("la sale guerre") by supporters of the Left in France and intellectuals (including Sartre) during the Henri Martin Affair in 1950.
The French had the strategy of pushing Việt Minh into attacking a well defended base in a remote part of the country at the end of the logistical trail. This strategy was validated at the Battle of Na San. The big problem of the war was the lack of construction materials (especially concrete). Because of difficult terrain without roads, tanks could not be used, and providing air cover was difficult. That made it almost impossible to defend the area effictively.
Dien Bien Phu.
The battle started when the French army tried to attack the Viet Minh after cutting of the supply line to get a easy defeat. The Viet Minh surrounded the French army with trenches and attacked using artillery. With the trenches the battle looked like a battle from World War 1. The French wanted to resupply the troops from the air but there were anti-aircraft guns that shot down the planes. The Viet Minh with all these advangtages won the battle, which caused the war to end shortly afterwards.
End of war.
After the war, the Geneva Conference on July 21, 1954 made a provisional division of Vietnam at the 17th parallel. The Việt Minh received control over the north in a territory called Democratic Republic of Vietnam, under Hồ Chí Minh. The area south of the 17th parallel was turned into State of Vietnam, under Emperor Bảo Đại, to prevent Hồ Chí Minh from gaining control of the entire country. A year later, Bảo Đại would be deposed by his prime minister, Ngô Đình Diệm, creating the Republic of Vietnam. Diem's refusal to enter into negotiations with North Vietnam on holding nationwide elections in 1956, as had been suggested by the Geneva Conference, would lead to the war breaking out again in South Vietnam in 1959, the Second Indochina War.