sentences:  He ordered his ninth son, Liu Hongcao () to become "Bình Hải tướng quân" (Sea-Pacifying Military General) and "Giao Chỉ vương" (King of Giao Chỉ), he commanded the naval forces of the Southern Han into Giao Chỉ.In 937, Liu Yan (; ), the Southern Han ruler took the chance to intervene in Vietnam after the death of the Annam Lord Protector Dương Đình Nghệ.Liu Yan had been previously defeated by Dương Đình Nghệ in 931.