The Buddha had been very concerned about the social organization of the sangha, but he seems to have been less interested in presenting an organized system of religious thought. Rather, as he traveled around, he taught, answered questions, and addressed individual concerns and specific situations. His responses varied depending on the personal situation and needs of the individual he was addressing at any particular time. He might answer a monk striving for enlightenment in one way, but respond to a householder whose child was suffering from a debilitating illness in a different and apparently contradictory way.
Around four centuries after the Buddha's death, a new school of Buddhist thought began to develop that expanded on this concept that the Buddha taught different things to different people. Called the Mahayana, or Great Vehicle, these new ideas were presented in a proliferation of new writings. It was claimed that these new sutras had been hidden away until the time was right to share them more widely, and that they contained truths that the Buddha had taught secretly to those few who were ready to hear them.
The oldest texts had emphasized the Buddha's statement that he was not a god, but an ordinary man, and that what he had attained, anyone could attain. In Mahayana Buddhism, however, a view of the Buddha as a transcendent being emerged. The Mahayana sutras presented the notion of multiple universes and multiple Buddhas, including cosmic Buddhas who existed outside of human time, and bodhisattvas who would interact with humans to lead them toward enlightenment. The Buddha who had been Siddhartha Gautama was said to have never been human, but a perfected being who pretended to be human to inspire humanity.
There is no indication that Mahayana Buddhism began as a separate school. Rather, Mahayana was a point of view held by some monks and thinkers within Buddhist monasteries, and disputed by others. The Mahayana scholars argued that the ideal of becoming an arhat contradicted the Buddha's teaching of compassion. Instead, they argued, the goal of Buddhist practice should be to follow the path of the bodhisattva — to choose to postpone the ultimate dissolution of self, the attainment of Buddhist enlightenment, in order to devote oneself to the enlightenment of all as the Buddha himself had done. Whereas early Buddhism had focused on the goal of enlightenment only for rare individuals, the notion emerged in the Mahayana texts that all living beings could become enlightened.
An elaborate pantheon of deities evolved, some of whom were regarded as entities that had reached the status of bodhisattva and now existed to help others achieve enlightenment. Mahayana texts also introduced the idea of multiple Buddha realms occupied by multiple Buddhas, which led to scriptures about the potential for rebirth into these realms. Those who were ready could pursue the bodhisattva path, while those who were not yet ready could call upon the bodhisattvas for spiritual guidance and even assistance in worldly matters, and in death they could seek rebirth in one of these sacred realms. New philosophical concepts were also introduced in the Mahayana sutras, concepts that would become cornerstones of Buddhist philosophy, such as: emptiness, wisdom, compassion, and skillful means.
The disagreement between the Mahayana scholars and other, more traditional scholars eventually led to separate divisions of Buddhism. Although there were many sub-schools of Buddhism at the time of the emergence of the Mahayana (Buddhist texts say there were eighteen schools), the so-deemed "traditional" philosopher-monks eventually came to call their school the Theravada, or the "doctrine of the elders." Mahayana Buddhist polemicists called them Hinayana, or Lesser Vehicle, a pejorative term. Theravada would become the dominant form of Buddhism in Southeast Asia, and there an emphasis on the older, monastic traditions continued. As Buddhism spread through Central Asia to China, Korea, and Japan, however, it was the Mahayana sutras that had the greatest appeal. In these new regions, new texts continued to emerge and Mahayana Buddhism would continue to evolve over the centuries.
Eventually Theravada and Mahayana came to be regarded as two distinct divisions of Buddhism. A third emerged, known as the Vajrayana, the Diamond or Thunderbolt Vehicle. By the 8th and 9th centuries C.E., Vajrayana Buddhism had spread beyond India to much of Asia, but its practice is now limited mainly to Tibetan Buddhism, Shingon Buddhism in Japan, and some Korean and Japanese new religions.