The Tibetan expression of Buddhism (sometimes called Lamaism) developed in Tibet and the surrounding Himalayan region beginning in the 7th century CE.
Certain Buddhist scriptures arrived in southern Tibet from India as early as 173 CE during the reign of Thothori Nyantsen, the 28th king of Tibet. During the third century the scriptures were disseminated to northern Tibet. The influence of Buddhism was not great in Tibet, however, and was not yet in its characteristic Tantric form, for the earliest Tantras had just begun to be written in India.
The first significant event in the history of Tibetan Buddhism occurred in 641, when King Songtsen Gampo (c.609-650) unified Tibet and took two Buddhist wives (Princess Wencheng from China and Princess Bhrikuti Devi from Nepal). Before long, King Gampo made Buddhism the state religion and established a network of 108 Buddhist temples across the region, including the Jokhang and Ramoché temples to house the Buddha statues his wives had brought as their dowries. Conflict with the former national religion, Bön, however, would continue for centuries.
The most important event in Tibetan Buddhist history was the arrival of the great tantric mystic Padmasambhava in Tibet in 774 at the invitation of King Trisong Detsen. It was Padmasambhava (more commonly known in the region as Guru Rinpoche) who merged tantric Buddhism with the local Bön religion to form what we now recognize as Tibetan Buddhism. In addition to writing a number of important scriptures (some of which Tibetan Buddhists believe he hid for future monks to find at the right time), Padmasambhava established the Nyingma school from which all schools of Tibetan Buddhism are derived.
Tibetan Buddhism exerted a strong influence from the 11th century among the peoples of Central Asia, especially in Mongolia and Manchuria. It was adopted as an official state religion by the Mongol Yuan dynasty and the Manchu Qing dynasty of China.
Tibet remained independent until the early 1900s, when it was occupied first by Britain and then China. The Tibetans reasserted their independence from China in 1912 and retained it until 1951, when it was "liberated" by China. Today, Tibet is still occupied by China. The Dalai Lama, the spiritual and political leader of the Tibetan people, lives in exile in India, and Chinese officials outnumber Tibetans in their own homeland.
Tibetan Buddhism spread to the West in the second half of the 20th century as many Tibetan leaders were exiled from their homeland. Today, Tibetan religious communities in the West consist both of refugees from Tibet and westerners drawn to the Tibetan religious tradition.