Sri Lanka's Theravada Buddhist tradition played a crucial role in the estavlishment and development of Buddhism in Southeast Asia, particularly as monastic Buddhism had been on the decline in India, before the centres of Buddhist scholarship in the Ganges region finally fell victim to destruction during the Muslim invasions of the late 12th century. It was during this period that the empire of Bagan (Pagan) in Myanmar (Birma) reached is climax under King Chansu II (Sithu II, also known as Narapatisithu). Under his reign the young Buddhist monk Sapada (Chapata)travelled to Sri Lanka in order to study there and to receive a renewed higher ordination to introduce the Sinhalese line of succession in Myanmar. He was from the Mon ethnicitiy, which played a crucial role in transferring the Theravada tradition to the Bagan kingdom. His reform resulted in the establishment of a second order of Theravada Buddhism in Bagan, which became dominant in later centuries. During the 13th century, Sapada's followers, who initially caused only a kind of shism in the Theavada Buddhist culture of Bagan, were even more successfull in missionaries in the Menam region, where the newly established Thai (Siamese) kingdoms were gaining independence from Khmer hegemony. Hence, the Thai adapted the Sinhalese Mahavihara pattern of Theravada Buddhism and made it the official state religion, thereby intentionally turning away from the Hindu religion of the Khmer empire.
However, the Sapada mission and the Thai tradition of Theravada finally succeeded in the Khmer empire, too. According to some reports, one of the companions travelling with Sampada was a son of King Jayavarman VII, who was the first Buddhist king in Cambodia, but an adherent of Mahayanism. After Jayavarman VII's reign during the same period mentioned above, Hinduism had a royal revival in Cambodia inthe second half of the 13th century. But finally Theravada was successfull in Cambodia due to its appeal in rural villages. The Theravada teachings and monsatic line of the Sinhalese sect had been introduced in Cambodia in the course of the 13th century. Unlike Shivaism, Vishnuism, and Mahayana Buddhism, which were imposed from the empire’s elites, the new doctrine was mainly preached to common people. Khmer farmers during the centuries of Hindu and Buddhist state cults had remained to be animistic, sparcely touched by those foreign Indian religions of the Khmer elites. Instead of elaborate court ceremonias, the monks of the Sinhalese tradition prescribed meditation and were devoted to a life of modesty and austerity. Unlike the priestly hierarchy close to the royal family whose political power was in decline, the Theravada monks were in direct contact with ordinary people and managed to stimulate a popular movement. This carried the Khmers, too, into the Theravada fold, until the present day.
Nuwan Chinthaka Gajanayaka,