This is a study of the experiences of Vietnamese soldiers and workers who rallied behind the French flag during World War I and of the impact of the war on the French colonial enterprise in Indochina. In telling their stories, the author wants to present a balanced view of the relationship between the French and the Vietnamese subjects of this study. Without World War I, the path to revolution and to national independence would have taken a different direction. During the war tens of thousands of Vietnamese joined millions of French people, members of other colonies in the French Empire, and the soldiers of the Allied Forces in a “sacred union” against the Germans. Their experiences in Europe, however, changed their lives and their attitudes toward France and its people, altered the course of the colonial enterprise, and gave rise to a new Vietnamese social class in France and in Indochina, which ultimately challenged French authority and brought changes to the established order in Indochina.