Original: Between the 17th century and 1959, the lines of Dalai Lamas were the head of the Tibetan Government, administering a large portion of the area from the capital Lhasa, although the extent of the lineage's political authority and rulership over territory has been contested.
Simplified: Between the 17th century and 1959, the Dalai Lama was the head of the Tibetan government.