The Mahayana (Great Vehicle) school added the concept of Bodhisattva as divine savior, and was then the most dominant form of Buddhism, spreading to China and Japan.
Japan and China outlawed Buddhism. 
mnli hypothesis: Japan and China outlawed Buddhism.  premise: The Mahayana (Great Vehicle) school added the concept of Bodhisattva as divine savior, and was then the most dominant form of Buddhism, spreading to China and Japan.