Buddhism began with a single human being's discovery — Siddhartha Gautama, under a Bodhi tree in northern India around 500 BCE — that suffering arises from craving and aversion, and that there is a path out. The simplicity of this insight belies its radicalism: if suffering is caused by the mind's relationship to experience rather than by experience itself, then liberation is possible in this lifetime, regardless of caste, gender, or circumstance. From this single insight grew one of the world's most intellectually sophisticated and geographically widespread spiritual traditions.
The Buddha's first teaching after his enlightenment was a medical diagnosis: Dukkha — suffering, unsatisfactoriness, the pervasive sense that something is wrong — is the fundamental characteristic of unexamined existence. Samudaya: suffering arises from craving (tanha) — the grasping after pleasant experience and the pushing away of unpleasant. Nirodha: there is cessation — craving can end, and with it, suffering. Magga: the Eightfold Path is the way to that cessation.
Theravada — the Way of the Elders — preserves what it considers the earliest Buddhist teachings in the Pali Canon. Its ideal is the arahant who achieves nirvana through individual practice. Dominant in Sri Lanka, Thailand, Myanmar, Cambodia, and Laos.
Mahayana — the Great Vehicle — extended the Buddhist ideal to the bodhisattva who delays their own final liberation to return and help all beings achieve liberation first. Its philosophical traditions — Madhyamaka (emptiness), Yogacara (mind-only) — are among the most rigorous in philosophy. Dominant in China, Japan, Korea, and Vietnam.
Vajrayana — the Diamond Vehicle — is the tantric Buddhism of Tibet, Nepal, and Mongolia. It uses ritual, visualisation, mantra, and the recognition of awareness itself as the ground of liberation. The Dalai Lama tradition and the Tibetan Book of the Dead are its best-known expressions.
Three things cannot be long hidden: the sun, the moon, and the truth. — Attributed to the Buddha