Japan occupies Vietnam temporarily, after defeating the French during WWII. After WWII, the French come back and Vietnam gets divided into North and South Vietnam at the 17th parallel. Ho Chi Minh becomes the leader in the North. The French support ex-Emperor Bao Dai in the South, but the US supports his Premier Ngo Dinh Diem. The conflict starts when the US refuses to hold elections in 1956 per the Geneva Accords of 1954.