Explanation:

In the third century B.C., there was disagreement among Ceylonese monks about the differences in practices between some councils of Bhikkhu monks and Vajjian Monks. The Bhikkhu monks affirmed Theravada traditions and rejected some of the practices of the Vajjian monks. It is thought that this sparked the split between Theravada and Mahayana Buddhism.
Theravada Buddhism was formed and developed by Ceylon Bhikkhus during a period spanning from the third century B.C. to fifth century A.D. Ceylonese influence, however, did not reach Southeast Asia until the eleventh century A.D. Theravada Buddhism developed in Southern India and then traveled through Sri Lanka, Burma, and into Thailand, Cambodia, Laos and Beyond.