The French lost the First Indochina for a variety of reasons, such as the inability to match the Vietnamese War machine, lack of vision regarding the end of colonialism and independence for Vietnam, and finally the disaster which was Dien Bien Phu and the reaction at home.
The French had controlled the country from the 1850's up until 1940 when during WWII Japan moved into Indochina, taking control of the country, but leaving it under the rule of the French. In 1945 Japan looked as if it was defeated and so announced Independence for Vietnam. The French were now intending to reclaim territory which they considered rightfully theirs as colonial land, using their conventional, modern day military system which had won the Allies World War I.
The Vietnamese, for the best part of the conflict represented by the Viet Minh were tired of Colonial oppression, and following Japans announcement on an Independent State of Vietnam, The Viet Minh, under the leadership of Ho Chi Minh were quick to announce themselves as the rulers of the newly formed "Democratic Republic of Vietnam".
During Japans occupation of Vietnam the Viet Minh had been creating a political and social structure in the North of the Country to deliberately resist the inevitable return of the French to reclaim what they considered rightfully theirs. In comparison to Frances army, the Viet Minh appeared to be a far more primitive army, using older weapons, but that didn't mean they were going to lose the war.
Initially, the French moved into Vietnam with assistance from Britain and China to disarm the Japanese. However in the North the Chinese didn't recognise French Colonialism in Asia, so on top of disarming the Japanese the Chinese also armed the Viet Minh, preparing them for a conflict with the...