In the 3d cent. B.C. the Indian emperor Asoka greatly strengthened Buddhism by his support and sent Buddhist missionaries as far afield as Syria. In succeeding centuries, however, the Hindu revival initiated the gradual decline of Buddhism in India. The invasions of the White Huns (6th cent.) and the Muslims (11th cent.) were also significant factors behind the virtual extinction of Buddhism in India by the 13th cent.
In the meantime, however, its beliefs had spread widely. Sri Lanka was converted to Buddhism in the 3d cent. B.C., and Buddhism has remained its national religion. After taking up residence in Sri Lanka, the Indian Buddhist scholar Buddhaghosa (5th cent. A.D.) produced some of Theravada Buddhism's most important scholastic writings. In the 7th cent. Buddhism entered Tibet, where it has flourished, drawing its philosophical influences mainly from the Madhyamika, and its practices from the Tantra.
Buddhism came to SE Asia in the first five centuries A.D. All Buddhist schools were initially established, but the surviving forms today are mostly Theravada. About the 1st cent. A.D. Buddhism entered China along trade routes from central Asia, initiating a four-century period of gradual assimilation. In the 3d and 4th cent. Buddhist concepts were interpreted by analogy with indigenous ideas, mainly Taoist, but the work of the great translators Kumarajiva and Hsüan-tsang provided the basis for better understanding of Buddhist concepts.
The 6th cent. saw the development of the great philosophical schools, each centering on a certain scripture and having a lineage of teachers. Two such schools, the T'ien-t'ai and the Hua-Yen, hierarchically arranged the widely varying scriptures and doctrines that had come to China from India, giving preeminence to their own school and scripture. Branches of Madhyamika and Yogacara were also founded. The two great nonacademic sects were Ch'an or Zen Buddhism, whose chief practice was sitting in meditation to achieve "sudden enlightenment," and Pure Land Buddhism, which advocated repetition of the name of the Buddha Amitabha to attain rebirth in his paradise.
Chinese Buddhism encountered resistance from Confucianism and Taoism, and opposition from the government, which was threatened by the growing power of the tax-exempt sangha. The great persecution by the emperor Wu-tsung (845) dealt Chinese Buddhism a blow from which it never fully recovered. The only schools that retained vitality were Zen and Pure Land, which increasingly fused with one another and with the native traditions, and after the decline of Buddhism in India, neo-Confucianism rose to intellectual and cultural dominance.
From China and Korea, Buddhism came to Japan. Schools of philosophy and monastic discipline were transmitted first (6th cent.–8th cent.), but during the Heian period (794–1185) a conservative form of Tantric Buddhism became widely popular among the nobility. Zen and Pure Land grew to become popular movements after the 13th cent. After World War II new sects arose in Japan, such as the Soka Gakkai, an outgrowth of the nationalistic sect founded by Nichiren (1222–82), and the Risshokoseikai, attracting many followers.