•what caused the shift from hinduism to buddhism

If you mean in India specifically or in other countries as well? For the most part, Buddhism became increasingly popular in India between after 300 b.c, especially with Emperor Ashoka, who embraced Buddhism and helped facilitate its expansion. Hinduism, however, has been and continues to be the dominant religion in the country. A small wave of Buddhism spread south to Sri Lanka, but the largest wave of Buddhism spread across the Himalayas into Tibet and China, then from China to Japan and Korea.

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