Tonkin (Tongking) was a former region of Vietnam, on the China Sea. It was under Chinese rule from 111 BC and became independent in 939 and remained self-governing until the 19th century when it became a part of French Indochina from 1885-1946. It's capital was Hanoi, and it became a part of North Vietnam from 1954 and was merged into Vietnam after the Vietnam War. Research Tonkin