Economy of Vietnam
Until the French colonization in the mid-19th century, Vietnam's economy had been mostly agrarian, subsistence-based and village-oriented. French colonizers, however, deliberately developed the regions differently as the French needed raw materials and a market for French manufactured goods, designating the South for agricultural production as it was better suited for agriculture, and the North for manufacturing as it was naturally wealthy in mineral resources. Though the plan exaggerated regional divisions, the development of exports—coal from the North, rice from the South—and the importation of French manufactured goods stimulated domestic commerce.
French language in Vietnam
The influence of the French language in Vietnam slowly began to decline after World War II as revolutionary movements increased and their works began to be written more in Vietnamese. Poorer and generally, more rural populations began to resist French rule and guerrilla forces, the Viet Minh attacked the French and sparked the First Indochina War. 
The French language however, continued its presence in government, education and media in areas not held by the Viet Minh. At the Battle of Dien Bien Phu in 1954, the Viet Minh defeated the French and Vietnam gained its independence, though the nation was soon divided into a communist, Soviet-oriented north, and a free government in the south. Fearing persecution by the communist government, hundreds of thousands fled to the south, including French-educated and speaking elite. Despite the Vietnam War erupting shortly afterwards, French continued a healthy presence in South Vietnam, where it was an administrative and educational language. The sharpest decline of the French language in Vietnam was after the Fall of Saigon in 1975 as the communist government imposed Vietnamese as the sole official and educational language on the entire nation, including the south, which was in a transitional phase until 1976.