Vietnam had been conquered by China in the 2nd century BC. The Chinese however, were unable to absorb the Vietnamese, who managed to maintian there own ways. In 939 after a number of abortive attempts the Vietnamese managed to acheive independence from China. The Vietnamese called their state Dai Viet. As it expanded it came into continued conflict with its neighbor to the south Campa. Over the years each side gained victories over the other, but by the 15th century Champa was conquered. Vietnam faced a number of threats from the North however. It successfully repelled two Mongol invasions.