The French wanted to reassert their control over Vietnam. Challenging them was a powerful nationalist movement within Vietnam committed to creating an independent nation.
The nationalists were organised into a political party, the Vietminh, which had been created in 1941
It was led by Ho Chi Minh. He was a communist educated in Paris and Moscow, and a fervent Vietnamese nationalist.
The Vietminh had fought against Japan throughout World War II.
After the fall of Japan in 1945, the Vietminh declared Vietnam an independent nation and set up a nationalist government under Ho Chi Minh in Hanoi. This was before the Western powers had time to return.