Seizing this chance, Zhabdrung's followers rallied and ousted the Tibetans from their territory, turning the battle into a decisive strategic victory of Ngawang Namgyal, paving the way for the Unification of Bhutan under his rule.

As result of a theological and political dispute in Tibet over the reincarnation of the Drukpa Lineage-holder in the early 17th century, there were two men who claimed to be the rightful 18th abbot of Ralung Monastery: Ngawang Namgyal and Gyalwang Pagsam Wangpo.

The conflict eventually escalated, and Ngawang Namgyal, whose "high level of intelligence, charisma and ambition were perceived as significant threats to the establishment", chose to go into voluntary exile in 1616/17.

As their own efforts to remove Zhabdrung failed, the lamas appealed for the new Tsangpa ruler, Karma Tenkyong, to launch another invasion of Bhutan to overthrow their rival.

Why the Tsangpa dynasty also occupied Bumthang is unknown, but John A. Ardussi speculates that either Ngawang Namgyal had a large following there or that the Tibetans at least believed it to be so.

Deputing his political and military duties to his confidant Tenzin Drukgyal, Ngawang Namgyal retreated to Jarogang in Khothangkha, resolved to escape to India if his domain would be destroyed.

[5] After their victory at Simtokha Dzong, Ngawang Namgyal and his followers also expelled the Barawa monks from their strongholds in the Gasa valley, eliminating one rival sect from Bhutan for good.

After he found one, the foundation for the new Punakha Dzong was laid in 1637;[24] after its completion it remained the administrative centre and the seat of the Government of Bhutan until 1955, when the capital was moved to Thimphu.

[4] While Ngawang Namgyal continued to unify Bhutan, the Tibetans and their dissident Bhutanese allies launched one last invasion in 1639, but this war quickly turned into a stalemate.