Its decline lasted from the mid-14th until the 15th century. In 1378, the Ayutthaya King Borommaracha I subdued Sukhothai's frontier city of Chakangrao [Kamphaengphet], and henceforth Sukhothai became a tributary state of Ayutthaya. Sukhothai later attempted to break loose from Ayutthaya but with no real success, until in the 15th century it was incorporated into the Ayutthaya kingdom as a province. The focus of Thai history and politics now moved to the central plains of present-day Thailand, where Ayutthaya was establishing itself as a centralized state, its power outstripping not only Sukhothai but also other neighbouring states such as Suphannaphum and Lawo [Lopburi]