Did you know Tibet once controlled an empire? It ruled the Himalayan highlands, Bengal, and the modern Chinese provinces of Gansu and Yunnan from 618 CE to about 840 CE. Between the first and third emperor, their territory expanded eventually to the height shown in the map above. But difficulty of transportation and communication, and religious tensions due to the introduction of Buddhism in the early 700s CE, led to infighting which pitted the royal family against ancient noble families and supporters of the new religion.
The last two emperors were assassinated, one by pro-native religionists, one by a Buddhist hermit. Yes, a Buddhist assassinated an emperor. After the death of the tenth emperor, the Tibetan Empire disintegrated into civil war.