 During the emergence of Bhutan as an independent state in the 17th century, Shabdrung Ngawang Namgyal conquered the western valleys and constructed dzong fortresses to repel invasions from Tibet.His lieutenant, Penlop of Trongsa Mingyur Tenpa, went on to conquer the valleys in central and eastern Bhutan for the new theocratic government.As a result, each major valley contains a dzong fortress.