The Vietnamese waged war against the southern kingdom of Champa, continuing the Vietnamese long history of southern expansion (known as Nam tiến) that had begun shortly after gaining independence in the 10th century. Often, they encountered strong resistance from the Chams. After the successful alliance with Champa during the Mongol invasion, king Trần Nhân Tông of Đại Việt gained two Champa provinces, located around present-day Huế, through the peaceful means of the political marriage of Princess Huyền Trân to Cham king Jaya Simhavarman III. Not long after the nuptials, the king died, and the princess returned to her northern home in order to avoid a Cham custom that would have required her to join her husband in death.^[165] In 1307, the new Cham king Simhavarman IV (r. 1307–1312), set out to retake the two provinces to protest against the Vietnamese agreement but was defeated and taken as a prisoner. Champa became a Vietnamese vassal state in 1312.^[166] The Cham revolted in 1318. In 1326 they managed to defeat the Vietnamese and reasserted independence.^[167] Royal upheaval within the Cham court resumed until 1360, when a strong Cham king was enthroned, known as Po Binasuor (r. 1360–90). During his thirty-year reign, Champa gained its momentum peak. Po Binasuor annihilated the Vietnamese invaders in 1377, ransacked Hanoi in 1371, 1378, 1379, and 1383, nearly had united all Vietnam for the first time by the 1380s.^[168] During a naval battle in early 1390, the Cham conqueror however was killed by Vietnamese firearm units, thus ending the short-lived rising period of the Cham kingdom. During the next decades, Champa returned to its status quo of peace. After much warfare and dismal conflicts, king Indravarman VI (r. 1400–41) reestablished relations with the second kingdom of Dai Viet's ruler Le Loi in 1428.^[169]