Ayutthaya began its hegemony by conquering northern kingdoms and city-states like Sukhothai,[4]:222 Kamphaeng Phet and Phitsanulok. Before the end of the fifteenth century, Ayutthaya launched attacks on Angkor, the classical great power of the region. Angkor's influence eventually faded from the Chao Phraya River Plain while Ayutthaya became a new great power.
The emerging Kingdom of Ayutthaya was also growing powerful. Relations between the Ayutthaya and Lan Na had worsened since the Ayutthayan support of Thau Choi's rebellion In 1451, Yuttitthira, a noble of the Kingdom of Sukhothai who had conflicts with Borommatrailokkanat of Ayutthaya, gave himself to Tilokaraj. Yuttitthira urged Borommatrailokkanat to invade Phitsanulok, igniting the Ayutthaya-Lan Na War over the Upper Chao Phraya valley (the Kingdom of Sukhothai). In 1460, the governor of Chaliang surrendered to Tilokaraj. Borommatrailokkanat then used a new strategy and concentrated on the wars with Lanna by moving the capital to Phitsanulok. Lan Na suffered setbacks and Tilokaraj eventually sued for peace in 1475.
However, the kingdom of Ayutthaya was not a unified state but rather a patchwork of self-governing principalities and tributary provinces owing allegiance to the king of Ayutthaya under The Circle of Power, or the mandala system, as some scholars suggested .[5] These principalities might be ruled by members of the royal family of Ayutthaya, or by local rulers who had their own independent armies, having a duty to assist the capital when war or invasion occurred. However, it was evident that from time to time local revolts, led by local princes or kings, took place. Ayutthaya had to suppress them.
1686 French Map of Siam
Due to the lack of succession law and a strong concept of meritocracy, whenever the succession was in dispute, princely governors or powerful dignitaries claiming their merit gathered their forces and moved on the capital to press their claims, culminating in several bloody coups.[6]