Around 620 CE, the clans around Lhasa unified, then annexed, the ancient neighbouring kingdom of Zhangzung. The empire they founded expanded northward at the expense of the Chinese Tang Dynasty, occupying the Tarim Basin, before losing most of its gains under the irresolute rule of Emperor ‘Old Hairy’ Tride Tsuktsän. In the dying years of Tsuktsän’s reign, the Tibetans allied with the Abbasid caliphate to defeat the Tang at the Battle of Talas (751) on the Syr Darya. Trisong Detsen (r. 756–97) extended Tibetan rule into Nanzhao, and exercised suzerainty over the Pala Empire on the Bay of Bengal. However, upon his death, the empire was sapped by a protracted war with the Abbasids, and, increasingly, by internal sectarian strife, which culminated in the assassination of the last emperor Langdarma by a Buddhist monk, leading to the long ‘Era of Fragmentation’ and the empire’s rapid collapse into warring factions.
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