Or Tongking; Former region of Vietnam, on the China Sea; area 103,500 sq km/39,951 sq mi. Under Chinese rule from 111 BC, Tonkin became independent AD 939 and remained self-governing until the 19th century. A part of French Indochina 1885–1946, capital Hanoi, it was part of North Vietnam from 1954 and was merged into Vietnam after the Vietnam War.