This article records tradition as it has been passed down and reported. Its sources are not yet part of the atlas's verified catalogue.
Theravada Buddhism consolidates as the dominant tradition across mainland Southeast Asia from the eleventh century onward, in a region where Mahayana Buddhism and Hindu court traditions had earlier been prominent. The reform drew on Sri Lanka's own sangha reforms and on an older Theravada heritage already preserved among the Mon of southern Myanmar, so the consolidation carried an established lineage forward rather than introducing something wholly new.
King Anawrahta's unification of Myanmar under Theravada patronage from 1044 gave the reform its first state backing, the same royal sponsorship pattern that had carried Buddhism into Sri Lanka centuries earlier. Over the following two and a half centuries the same reform tradition spread into Thailand, then into Cambodia and Laos, court by court, until Theravada stood as the region's dominant religion.
What changed for the tradition's spread is a mainland Southeast Asian bloc unified under one shared form of Buddhism rather than several competing traditions, a position Cambodia, Myanmar, Thailand and Laos all still hold today as their own state supported religion, and this atlas records the outcome as dominant, the strongest of the spread status readings it tracks.