The emperor's minister, Myang Mangpoje (Myang Mang-po-rje Zhang-shang), defeated the Sumpa people ca. He was succeeded by minister Gar Songtsen (Mgar-srong-rtsan).The Chinese records mention an envoy to Tibet in 634.
After a Tibetan campaign against China in 635-6,) 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).
From the time of the emperor Songtsen Gampo the power of the empire gradually increased over a diverse terrain.
By the reign of the emperor Ralpacan, in the opening years of the 9th century, it controlled territories extending from the Tarim basin to the Himalayas and Bengal, and from the Pamirs to what is now Chinese provinces of Gansu and Yunnan.
The Chinese Princess Wencheng (Tibetan: Mung-chang Kung-co) departed China in 640 to marry Songtsen Gampo's son. 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.