Emergence of the Vajrayāna:

There are differing views as to just when Vajrayāna and its tantric practice started. In the Tibetan tradition, it is claimed that the historical Śākyamuni Buddha taught tantra, but as these are esoteric teachings, they were written down long after the Buddha's other teachings. Nālandā University became a center for the development of Vajrayāna theory and continued as the source of leading-edge Vajrayāna practices up through the 11th century. These practices, scriptures and theory were transmitted to China, Tibet, Indochina and Southeast Asia. China generally received Indian transmission up to the 11th century including tantric practice, while a vast amount of what is considered to be Tibetan Buddhism (Vajrayāna) stems from the late (9th–12th century) Nālandā tradition.

In one of the first major contemporary academic treatises on the subject, Fairfield University professor Ronald M. Davidson argues that the rise of Vajrayana was in part a reaction to the changing political climate in India at the time. With the fall of the Gupta dynasty, in an increasingly fractious political environment, institutional Buddhism had difficulty attracting patronage, and the folk movement led by siddhas became more prominent. After perhaps two hundred years, it had begun to get integrated into the monastic establishment.

Vajrayana combined and developed a variety of elements, a number of which had already existed for centuries.

Although it continued to in surrounding countries, over the centuries Buddhism gradually declined in India and it was virtually extinct there by the time of the British conquest.