Books on the history of Tibetan Buddhism record the following legend of how Buddhism spread to Tibet: On one particular day in the 5th century, Lhathothori Nyantzan, forefather of the Tubo Kingdom, was resting on the summit of Yungbolhakang. He suddenly found several Buddhist treasures falling from the sky. While the Tubo King had no idea what they were for, a mysterious voice from the sky informed him that the 6th Tsampo (king) of the Tubo Kingdom would know the use of the objects.
According to historical documents, these treasures were brought to Tibet by Indians Buddhists. Upon seeing that Tibetans had no idea of their significance, the Indian monks had no choice but to secret them in a safe place and return to india. The fact remains that Buddhism did spread into Tibet during the reign of Tubo King Songtsan Gambo in the 7th century.
Songtsan Gambo did his best to establish friendly ties with neighboring countries in order to strengthen economic and cultural exchanges and learn from the advanced cultures of various races. In the process he married with Princess Khridzun of Nepal and Princess Wencheng of China's Tang Dynasty (618-907). Each princess journeyed to Tibet with a statue of Buddha, and once there set about building the Jokhang and Ramoge monasteries in Lhasa. Artisans accompanying the princess were involved in the construction of monasteries, and Buddhist monks in their tourages began translating Buddhist scriptures. Buddhism thus spread to Tibet from Nepal and Han areas.
Tibet reeled under power struggle for more than half a century following the death of Songtsan Gambo. Buddhism failed to flourish until Tride Zhotsan, great grandson of Songtsan Gambo, finally took power. In 710, Tride Zhotsan asked for the hand of and eventually married Princess Jincheng of the Tang Dynasty. The new bride moved the statue of Buddha, which Princess Wencheng brought to Tibet, to the Jokhang Monastery. Meanwhile, she arranged monks accompanying her to the Tubo Kingdom to take in charge of the monastery and related religious activities. She engaged in a painstaking effort and finally succeeding in persuading the Tubo court to accept monks fleeing from Western Regions and build seven monasteries to house them. While the measures further boosted the development of Buddhism in Tibet, they nonetheless sparked discontent amongst ministers worshipping the Bon religion. The ministers left no stone unturned to obstruct the development of Buddhism, with to situation lasting until Trisong Detsan, the son of Tride Zhotsan, came to power.
Trison Detsan relied on Buddhism to fight ministers who rallied behind the Bon religion. As part of the effort, he invited Zhibatsho and Padmasambhava, famous Indian monks, to build the Samye Monastery in 799. Seven noble children were later tonsured to the monastery, which became the first monastery in Tibetan Buddhist history to tonsure monks. The event thus pioneered the tonsure system of Tibetan Buddhism.
In addition to inviting Indian monks to Tibet, Trisong Destan sent trusted emissaries to China's hinterland to invite monks to lecture in Tibet. Mahayana became one of the many Han monks who contributed to ensuring that Han Buddhism flourished in Tibet. Mahayana remained in Tibet for 11 years lecturing on Buddhism and completing nine books on Buddhist tenets.
Tubo kings in ensuing dynasties did their utmost to promote Buddhism by building monasteries and commissioning the translation of Buddhist sutras. At the same time, they granted monks royal incomes and even encouraged them to become involved in government affairs in order to undermine ministers who supported the Bon religion. The policy spawned the deep hatred of said ministers, who eventually arranged for the assassination of Tritso Detsan in 842. The ministers threw their support behind Darma, the brother of Tritso Detsan, to become the new Tubo king. This was in turn followed by the large-scale suppression of Buddhism in the region.
Shortly after assuming power, Darma set out to suppress Buddhism, but was soon assassinated by Tibetan Buddhists, and war erupted between the different power factions. Slaves, who were thrown into the abyss of misery, rose to revolt. Tibet was torn apart by various forces. The “diffusion of Buddhism” was thus halted.
The early 10th century witnessed the entry of a feudal society in tibet, with each of the Tubo ministers occupying a part of the kingdom and becoming feudal powers in their respective localities. They proceeded to promote Buddhism in order to strengthen their own rule. Buddhism was thus revived in Tibet. In terms of form and content, however, Buddhism rising in Tibet during tit particular period was worlds apart from Tubo Buddhism. The 300-odd years of struggle between Buddhism and the Bon religion resulted in each absorbing the strong points of the other. Buddhism became increasingly Tibetanized as the region entered the feudal stage. Tibetan Buddhism emerged and entered a stage of rapid development.