Tonkin is the northernmost of the three principal regions, from French Indochina, which made up what was to become Vietnam. Its key feature is the Red River Delta.
Pike sees northerners as thinking of themselves as modern, rational, efficient, and industrious. To him, southerners of Cochin China are rustics and Annamites from the center as traditionalists, stuck in the past, and focused on intrigue rather than achievement. 
- Pike, Douglas (1969), War, Peace and the Viet Cong, MIT Press, p.54