Um.... YOU need to go back and relearn your history. There was NO nation of Vietnam in 1920. What is today Vietnam was part of the French colony of Indochina which also incorporated what is today Laos and Cambodia.
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If you wil look on the God damned maps of the period, you will see three separate independent countries, Cochin-China in the extreme South, An Nam translated pacified south from the anchient Chinese, and Ton Kin in the North, from when the name Tonkin Gulf. They were separated from each other as well as from Laos and Cambodia. The area developed its own culture and written language under the influences of the Jesuits in the 1600s. The area was widely neglected and of little interest except for two things. The French lost out in colonization to the British who got the good stuff such as India and America. Consequently the French got the uncontested backwater such as parts of Africa nd SE Asia.
With the advent of the importance of rubber, the area became important and became inhabited by French plantation owners. The Farench attempted facilitation of rubber commerce through development of rails and roads north to south through the three countries. During the war, the Japanese needed SE Asia for the rubber, which brought conflict to the area. America had developed its synthetic rubber source through the GRS process derived from Corothers.
After the war the GRS process made the entire area obsolete. The American OSS armed communist Ho Chi Minh in alliance against the Japanese. After the war, the organized communist forces then turned upon the French in Ton Kin. The french were reluctant dragons in this new conflict. Ho Chi Minh took power in Ton Kin. Ho wiped out several entire cities in Ton Kin to do so. Non-Communist Catholics were exterminated.
When Co-Chin China and An Nam agreed to consolidate into a single nation under Bo Dai, Ho Chi Minh refused to recognize the agreement and made plans to invade from the separate nation of Ton Kin --which we erroneiousl called North Viet Nam over here. He was looking for an excuse to extend the communist revolution. ...and so forth. That's as much as I have time for.
Frankly, you don't seem to know jack shit about anything to do with the area or the war.