About 2,000 years ago Buddhism divided into two major schools: Theravada and Mahayana. For centuries, Theravada has been the dominant form of Buddhism in Sri Lanka, Thailand, Cambodia, Burma, (Myanmar) and Laos. Mahayana is dominant in China, Japan, Taiwan, Tibet, Nepal, Mongolia, Korea, and Vietnam. In recent years, Mahayana also has gained many followers in India. Mahayana is further divided into many sub-schools, such as Pure Land and Theravada Buddhism.
Vajrayana Buddhism, which is chiefly associated with Tibetan Buddhism, is sometimes described as a third major school. However, all schools of Vajrayana are also part of Mahayana.
The two schools differ primarily in their understanding of a doctrine called "anatman" or "anatta." According to this doctrine, there is no "self" in the sense of a permanent, integral, autonomous being within an individual existence. Anatman is a difficult teaching to understand, but understanding it is essential to making sense of Buddhism.
Basically, Theravada considers anatman to mean that an individual's ego or personality is a delusion. Once freed of this delusion, the individual can enjoy the bliss of Nirvana. Mahayana pushes anatman further. In Mahayana, all phenomena are void of intrinsic identity and take identity only in relation to other phenomena. There is neither reality nor unreality, only relativity. The Mahayana teaching is called "shunyata" or "emptiness."