I always thought that Tibet was a theocracy ruled by the reincarnation of the previous Dalai Lama, DL, from time immemorial.

However this conclusion seems is not entirely accurate. 

There apparently was another competing kingdom called the Guge:

http://en.people.cn/n/2015/0814/c205040-8936384.html

They do not know what happened for this kingdom to vanish; no record of it has ever been offered by the Potola Palace. 

That this is so, really leaves you to wonder if the previous incarnation of DL did not have some role to see in the extirpation of this kingdom and the erasure of its history.