By the 14th century, numerous chiefs ruled the Ryukyu Islands. In Okinawa, a new chief named Tamagusuku was unpopular among local lords, causing the island to be split into three kingdoms (Chūzan, Nanzan and Hokuzan). By the 15th century, the island was re-united, causing the Ryukyu Kingdom to be born. In the following centuries, the Ryukyu Kingdom would expand its rule over the Amami, Miyako and Yaeyama islands. They would also become a vassal state of China.