Robinson Richard, H., & Williard L. Johnson. 1997, The Buddhist Religion, A Historical Introduction, pp 141-153 Wadsworth Publishing Company
7.1 Orthodoxy and Syncretism, History and Culture
Theravada Buddhism has been preserved in Sri Lanka and in South East Asian Countries. Theravada is concerned with the quest for purity. Its royal patrons have sponsored over the centuries this search for purity through the Pali texts, pure ordination lines and encouragement of strict practices.
7.2 Buddhism in further India
In south east asia even though a Sri Lanka narrative tradition maintains that Emperor Asoka in 247 BCE sent missionaries to SavannaBhuma, identified as the Mon country in what is now Myammar and central Thailand, there is no archeological evidence supporting that Buddhism was present so early. It much more likely spread with Indian trade and by the 11th c CE various forms of Buddhism (Theravada, Sarvastivada, Mahayana and Vajrayana) coexisted with Hinduism and animism. By the late 8th c CE we can see Mahayana and Saivism, with Tantrism.
In Sri Lanka Buddhism came through the mission sent by Emperor Asoka, headed by his son Mahinda and his daughter Sangamita (who brought with her a shoot of the Boddhi tree to be planted as a relic offering). Sri Lanka over the centuries acquired the reputation of the pure teachings and attracted many monks and scholars. One of them in particular Bhuddaghosa left texts that today are regarded as more authoritative than the canon itself in Sri Lanka and Burma. Bhuddaghosa came from Karniciuram, and asked permission to translate the texts. The elders to test his knowledge asked him to compose a treatise in Buddhist practice. This treatise Viuddhimaga (The Path to Purification) along with the Pali commentaries of Bhuddaghosa are classic texts
7.3 The Theravada connection
There is a Theravada connection between Burma and Sri Lanka that was established in the beginning of the millennium and kept the Theravada Buddhism as the predominant form of Buddhism in these areas and later also Thailand. The benefits of this connection are (1) The connection established Sri Lanka as a prime center of Theravadin orthodoxy and Pali scholarship. (2) the canon and its commentaries became prime sources of inspiration, not only for the religious life of the area, but also in parts of secular culture and law. (3) The kings of Sri Lanka, Burma and Thailand maintained the lines of Buddhism alive within their countries which in turn kept stability in their societies.
7.4 The Colonial Period
The colonial period (16th – 20th c CE) affected the government’s religious policy. Moreover the spread of secular education and of Western Medicine deprived the monks of their traditional social roles.
7.4.1 Sri Lanka
Sri Lanka suffered the most from the colonial period. The Portuguese who first colonized Sri Lanka (1505-1658) destroyed monasteries, persecuted Buddhists and forcibly converted Buddhists to Catholicism. Under this pressure the king withdrew to Candy in the mountains, where they ruled from 1592-1815, supporting Buddhism only insofar as the circumstances would allow them to. In 1873 it was the Theosophical society leaders, Helena Blavatsy and Col. Henry Steel Olcott who took over the formation of the Protestan Buddhism movement, encouraging people to play an active role in the revival of Buddhism. This provided the model for the Buddhist movements of the 20th c CE. This movement became the rallying point for the nationalist anti-colonial cause.
The Burmese Sangha was better preserved through the colonialist period maybe because the English (1886-1948) had learned from their mistakes in Sri Lanka, or maybe because it was a shorter colonial period.
Thailand was never colonized yet the traditional roles in society for monks were displaced by the advent of secular education and Western medicine. The strength in the government though allowed the Sangha to stay outside politics (unlike Sri Lanka and Burma).