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Reign of Songtsen Gampo (618–650)

Songtsen Gampo (Srong-brtsan Sgam-po) (c. 604 – 650) was the first great emperor who expanded Tibet's power beyond Lhasa and the Yarlung Valley, and is traditionally credited with introducing Buddhism to Tibet.

When his father Namri Songtsen died by poisoning (circa 618), Songtsen Gampo took control after putting down a brief rebellion. Songtsen Gampo proved adept at diplomacy as well as combat. The emperor's minister, Myang Mangpoje (Myang Mang-po-rje Zhang-shang), defeated the Sumpa people ca. 627. Six years later (c. 632–33) Myang Mangpoje was accused of treason and executed. He was succeeded by minister Gar Tongtsen (mgar-stong-btsan).

The Chinese records mention an envoy to Tibet in 634. On that occasion, the Tibetan Emperor requested (demanded according to Tibetan sources) marriage to a Chinese princess but was refused. In 635-36 the Emperor attacked and defeated the Tuyuhun (Tibetan: ‘A zha), who lived around Lake Koko Nur and controlled important trade routes into China. After a series of military campaigns between Tibet and the Tang dynasty in 635-8, （see also Tibetan attack on Songzhou ）the Chinese emperor agreed (only because of the threat of force, according to Tibetan sources) to provide a Chinese princess to Songtsen Gampo.

Circa 639, after Songtsen Gampo had a dispute with his younger brother Tsänsong (Brtsan-srong), the younger brother was burned to death by his own minister Khäsreg (Mkha’s sregs) (presumably at the behest of his older brother the emperor).

The Chinese Princess Wencheng (Tibetan: Mung-chang Kung-co) departed China in 640 to marry Songtsen Gampo's son. She arrived a year later. This is traditionally credited with being the first time that Buddhism came to Tibet, but it is very unlikely Buddhism extended beyond foreigners at the court.

Songtsen Gampo’s sister Sämakar (Sad-mar-kar) was sent to marry Lig-myi-rhya, the king of Zhangzhung in what is now Western Tibet. However, when the king refused to consummate the marriage, she then helped her brother to defeat Lig myi-rhya and incorporate Zhangzhung into the Tibetan Empire. In 645, Songtsen Gampo overran the kingdom of Zhangzhung.

Songtsen Gampo died in 650. He was succeeded by his infant grandson Trimang Lön (Khri-mang-slon). Real power was left in the hands of the minister Gar Tongtsen. There is some confusion as to whether Central Tibet conquered Zhangzhung during the reign of Songtsen Gampo or in the reign of Trisong Detsen, (r. 755 until 797 or 804). The records of the Tang Annals do, however, seem to clearly place these events in the reign of Songtsen Gampo for they say that in 634, Zhangzhung and various Qiang tribes "altogether submitted to him." Following this, he united with the country of Zhangzhung to defeat the Tuyuhun, then conquered two more Qiang tribes before threatening the Chinese region of Songzhou with a very large army (according to Tibetan sources 100,000; according to the Chinese more than 200,000 men). He then sent an envoy with gifts of gold and silk to the Chinese emperor to ask for a Chinese princess in marriage and, when refused, attacked Songzhou. According to the Tang Annals, he finally retreated and apologised, after which the emperor granted his request.

After the death of Songtsen Gampo in 650 AD, the Chinese Tang dynasty attacked and took control of the Tibetan capital Lhasa. Soldiers of the Tang dynasty could not sustain their presence in the hostile environment of the Tibetan Plateau and soon returned to China proper."