Minor Reigns (1309 - 1431 A.D.)
Since the reign of Srindravarman, there were very rare historical records, especially of those successive kings following him in the 14th century. The last stele engraved in 1327 was in Pali and there was no more inscription found for the next two centuries. Perhaps the Khmer had changed their practice by writing on the unendurable materials such as the latina leaves and animal's skin rather than by engraving on the stones. Moreover, there were no more major temples or monuments built during this period. Their newly adopted religion of Theravada Buddhism could have played a major role here. As the king was no longer regarded as the god-king or "deva-raja", it was not necessary to build any massive mountain temple to house their gods and to represent the heavenly residence.
During this period, the Khmers were not able to maintain their vast and extensive irrigation systems efficiently. Various dikes and canals were silted up. The rice crops, previously used to be cultivated two to three times a year, dropped drastically since the Khmers could not prevent floods in Monsoon, and did not have enough water storage in the dry season. As productivity dropped, the empire was weaken. Probably, the kings lacked absolute power to mobilize sufficient laborers to maintain their irrigation system.
The first Thai kingdom of Suhkothai, emerged after the Khmers were driven out in the early 13th century, was later absorbed by another Thai state which was established as the Ayuthaya kingdom in 1351 by Ramathibodi I. The Ayuthaya kingdom became a major threat to Angkor Empire with its first attempt to attack the Angkor, but unsuccessfully in 1352. Several more attempts were made in the following years. Not until 1431, the large Thai army marched on the road, built by the last greatest Khmer king Jayavarman VII, from Chao Phaya River Basin through Aranyapathet to attack right at the heart of Angkor and sacked the city that same year. This marked the end of Angkor Empire.