The Second Tibetan Invasion of Bhutan or the Second Battle of Simtokha Dzong was a military confrontation in 1634 between the supporters of Zhabdrung Ngawang Namgyal and the forces of the Tibetan Tsangpa dynasty and several Bhutanese lamas allied against him. The latter initially conquered Zhabdrung’s seat, Simtokha Dzong, threatening to eliminate his young dominion. The castle’s ammunition stores were accidentally ignited during the battle, however, resulting in an explosion that destroyed Simtokha Dzong and much of the Tibetan army. 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.