Trishong Detsen - The Tibetan Emperor

There was a Tibetan king, Tibetan Emperor called Trishong Detsen who lived in the 8th and 9th centuries. He took control of the government when he attained his majority. In 755, China had begun to be weakened because of the Anshi rebellion started by An Lushan. From that time onwards, the Tibetans pressed into the territory of the Tang Emperors,. reaching the Chinese capital Changan which is modern day Shian in late 763 AD. But they did not take the he did not take Beijing. And eventually they turned on the Tibetan overlords and helped the Chinese defeat them.