Just how Asia’s various forms of Buddhism relate to one another is a difficult question. In part, their relationship is developmental. The Theravada (School of the Elders) claims to be the oldest tradition. It focuses on progress towards Enlightenment through the course of many lives. The Mahayana (Great Way) builds on Theravada teachings, but broadens its scope to aim at Enlightenment for all sentient beings as the highest good. The Vajrayana (Adamantine Way) adds to Theravada and Mahayana the knowledges and practices of tantra, aimed at speedy and efficacious transcendence through unorthodox means. Texts, deities, and practices of the three schools co-exist and commingle in most regions of Asia, and the situation is further complicated by the presence of other religions and belief systems in each locale. For present purposes it is perhaps enough to know that the Theravada is now predominant in Southeast Asia, Mahayana is characteristic in East Asia, and Vajrayana distinguishes the Himalayan region of South Asia.
The figure below maps the spread of Buddhism from the 4th century BC to the 6th century A.D. onto the three regions of modern Asia as construed in Cornell’s collections.