There was no central government during this period. Instead, small independent monarchies began to develop by the early 9th century. Each was ruled by a deb (king), some of whom claimed divine origins. The kingdom of Bumthang was the most prominent among these small entities. At the same time, Tibetan Buddhist monks (lam in Dzongkha, Bhutan's official national language) had firmly rooted their religion and culture in Bhutan, and members of joint Tibetan-Mongol military expeditions settled in fertile valleys. By the 11th century, all of Bhutan was occupied by Tibetan-Mongol military forces.