the castle's promontory as a dock, and later Unten harbor. Nevertheless, the northern kingdom engaged in its share of trade with many of the other states in the region, including Java, Sumatra, and the Ayutthaya Kingdom of Siam. Chūzan entered a tributary relationship with Ming dynasty China in 1372, and Hokuzan and Nanzan were granted similar commercial status shortly afterwards. Over roughly the next thirty years, only nine tribute missions were sent from Hokuzan to China; Nanzan sent nineteen and Chūzan sent fifty-two. Hokuzan also did not send any students to China, as Chūzan did. Roughly twenty years later, in the 1390s, the kings of all three kingdoms died within a few years, and succession disputes erupted across the island; similar events occurred in Nanking at the same time, with the death of the Hongwu Emperor in 1398. Previously, China had only ever recognized one head of state on Okinawa, but now all three kingdoms sent envoys and vied for the prestige, wealth, and power that would come with China's favor; no response came from China for eleven years. In 1406, Bunei, King of Chūzan, was formally invested by representatives of the Ming Court in his position; the kings of Hokuzan would never enjoy this privilege. Despite its economic and political advantages, Hokuzan posed a not insignificant threat to Chūzan, militarily, since its establishment. In the 1410s, however, disputes among the vassals of Hokuzan's king weakened the kingdom, and in 1416, Chūzan found an opportunity to strike after three of those vassals (anji) defected. Following a fierce defense, Nakijin castle fell, and the king and his closest vassals committed suicide. After the unification: Hokuzan-fu After the annexation of Sanhoku, Shō Hashi, king of Chūzan, appointed his second son Shō Chū the in 1422, a post which would remain for many years, holding little overall power, but serving to maintain order in the north on behalf of the Chūzan court at Shuri. The post was abolished by Shō Shitsu in 1665, the last warden was ordered to move to Shuri. During the Ryukyu Kingdom period, Hokuzan was one of three nominal of the kingdom without administrative function. At the end of the 17th century, Sanhoku nominally comprised 9 : Onna, Kin, Kushi, Nago, Haneji, Motobu, Nakijin, Ōgimi, and Kunigami. During King Shō Kei's reign, someone suggested that the capital should be moved to Nago. It was disapproved by the regent Sai