Cochin China, which includes the Mekong Delta, was the southernmost of the three main regions of French Indochina, which became Vietnam. Other variants on the name include "Cochinchina", "Cochin-China", or "Cochinchine".
After the Republic of Vietnam was formed, Cochin China, less Saigon, was roughly equivalent to IV Corps tactical zone. Nguyen Ngoc Tho, the vice-president under Ngo Dinh Diem and briefly premier after the overthrow of Diem, was prominent as one of the few Cochin Chinese in the Diem government.
Pike sees southerners as identifying as peaceful and in harmony with nature. Had the other regions had the patience of southerners, the French would have left as the British left india. He sees the Northerner as starting wars and the Central people as loving intrigue for its own sake. 
- Pike, Douglas (1969), War, Peace and the Viet Cong, MIT Press, p.54