Page "History of Bhutan" Paragraph 11

There was no central government during this period.

Instead, small independent monarchies began to develop by the early ninth 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 eleventh century, all of Bhutan was occupied by Tibetan-Mongol military forces.