 Complete the following phrase:  China and Vietnam had contact since the Chinese Warring States period and the Vietnamese Thục Dynasty in the 3rd century BC, as noted in the 15th-century Vietnamese historical record Đại Việt sử ký toàn thư. Between the 1st century BC and the 15th century AD, Vietnam was subject to four separate periods of imperial Chinese domination although it successfully asserted a degree of independence after the 