The first diffusion
Tibet in the 7th century was a rising military power. Songtsen Gampo, who died around 649, is credited with the first Buddhist temples in Lhasa, including the Jokhang, and with sending a minister to India to devise a script for writing Tibetan. How Buddhist he personally was is not clear from the records of his own time.
The decisive reign was that of Trisong Detsen, from about 755 to 797. He invited the Indian scholar Śāntarakṣita from Nālandā, founded the monastery of Samye around 779, and had the first Tibetans ordained as monks. Tradition adds the tantric master Padmasambhava, invited to deal with the obstacles the project met.
The debate at Samye
Tibetan accounts describe a contest held at Samye between two approaches: the gradual Indian path, argued by Kamalaśīla, and the sudden awakening taught by the Chinese Chan monk Moheyan. The Indian side was declared the winner, and Tibet's Buddhism was thereafter oriented towards India rather than China.
Historians treat the story with care. Tibetan and Chinese sources each claim victory for their own side, and the debate may have been a series of exchanges rather than a single event. What is not in doubt is the outcome: Tibetan Buddhism took its texts, its vocabulary and its curriculum from India.
Collapse, and a second beginning
Royal support ended in the 9th century under Langdarma, and the Tibetan empire broke apart soon after. Organised monastic Buddhism nearly disappeared from central Tibet for over a century, while surviving in the far east and west of the plateau.
From the late 10th century a second diffusion began, sponsored by the kings of Guge in western Tibet and by lineages in the east. This later wave produced most of what we now recognise as Tibetan Buddhism.
Why it matters
It begins Tibet's transformation into one of the major centres of the Buddhist world.
History and tradition
What historians can say
The Old Tibetan Annals and the Dunhuang manuscripts, together with royal edicts, confirm the sponsorship, the founding of Samye and the ordination of Tibetans. The later religious histories, such as Buton's in the 14th century, are devotional works written centuries after the events. Langdarma's persecution was probably the withdrawal of state funding rather than a campaign of violence; its scale is disputed.
What Buddhist tradition remembers
Nyingma tradition remembers Padmasambhava subduing the local deities of Tibet and binding them by oath to protect the Dharma, and hiding teachings as treasures, terma, to be found when they were needed.