The Ayutthaya kings adopted Khmer cultural influences from the very beginning. No longer the paternal and accessible rulers that the kings of Sukhothai had been, Ayutthaya's sovereigns were absolute monarchs and assumed the title devaraja (god-king). The early part of this period saw Ayutthaya extend its sovereignty over neighboring Thai principalities and come into conflict with its neighbors. During the 17th century, Siam started diplomatic and commercial relations with western countries. In 1767, after repeated attempts, the Burmese invaded and successfully captured Ayutthaya.
Despite their overwhelming victory, the Burmese did not retain control of Siam for long. A young general named Phya Taksin and his followers broke through the Burmese lines and escaped to Chantaburi. Seven months after the fall of Ayutthaya, he and his forces sailed back up the Chao Phraya River to Ayutthaya and expelled the Burmese occupation garrison, though tragically the capital had been looted and nearly razed.
By the end of the century, Ayutthaya was regarded as the strongest power in mainland Southeast Asia. Ayutthaya began its hegemony by conquering northern kingdoms and city-states like Sukhothai, Kamphaeng Phet and Phitsanuloke. 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.
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 . 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.
After a bloody period of dynastic struggle, Ayutthaya entered into what has been called the golden age, a relatively peaceful episode in the second quarter of the eighteenth century when art, literature, and learning flourished. There were foreign wars. Ayutthaya fought with the Nguyễn Lords(Vietnamese rulers of South Vietnam) for control of Cambodia starting around 1715. But a greater threat came from Burma, where the new Alaungpayadynasty had subdued the Shan states.
The ruins of the historic city of Ayutthaya and "associated historic towns" in the Ayutthaya historical park have been listed by the UNESCO as World Heritage Site. The city of Ayutthaya was refounded near the old city, and is now capital of the Ayutthaya province.