Traditional Tibetan history described the exploits of a lengthy list of rulers. External corroboration is available from the 7th century in Chinese histories. From the 7th to the 9th century a series of emperors ruled Tibet. 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 varied terrain of the empire and the difficulty of transportation, coupled with the new ideas that came into the empire as a result of its expansion, helped to create stresses and power blocs that were often in competition with the ruler at the center of the empire. Thus, for example, adherents of the Bön religion and the supporters of the ancient noble families gradually came to find themselves in competition with the recently introduced Buddhism. The empire collapsed into civil war in the 840s.
The power that became the Tibetan state originated at the Taktsé Castle (Wylie: Stag-rtse) in the Chingba (Phying-ba) district of Chonggyä (Phyongs-rgyas). There, according to the Old Tibetan Chronicle, a group convinced Tagbu Nyazig (Stag-bu snya-gzigs) to rebel against Gudri Zingpoje (Dgu-gri Zing-po-rje), who was in turn a vassal of the Zhangzhung empire under the Lig myi dynasty. The group prevailed against Zingpoje. At this point Namri Songtsen (also known as Namri Löntsän) was the leader of a clan which one by one prevailed over all his neighboring clans. He gained control of all the area around what is now Lhasa, before his assassination around 618. This new-born regional state would later become known as the Tibetan Empire. The government of Namri Songtsen sent two embassies to the Chinese Sui Dynasty in 608 and 609, marking the appearance of Tibet on the international scene.
The historic name for the Tibetan Empire is different from Tibet's present name.
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.