September 2 is National Day in Vietnam and commemorates the Vietnamese Declaration of Independence from France.
By 1945, Vietnam had been a colony of France for 87 years, called at that time French Indochina. Throughout WW2 Vietnam was used alternately by the French and the Japanese for their own interests with little concern for the welfare of the Vietnamese people. At the end of WW2, the Potsdam Conference divided Indochina into two zones at the sixteenth parallel, ceding southern zone to the Southeast Asian Allied Forces and the northern zone to Chiang Kai-Shek. Chiang, however, did not facilitate the French re-entry into Vietnam, as the Allies did, and French Indochina was basically re-established in the southern zone.
This schism led disastrously led the to Vietnamese/American War.
This map of Vietnam was created by Wikipedian ASDFGH who has released it into the public domain.