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. Prelude 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. Both were backed by different groups within the Drukpa sect, but the latter also enjoyed the support of the Tsangpa dynasty that dominated central Tibet at the time. 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. Invited by the lama of Gasa, he and his retinue settled down in the region that would later become western Bhutan. This area was at the time divided among several different chiefdoms, petty kingdoms and Buddhist sects that constantly fought for supremacy. Ngawang Namgyal was well received by the local Drukpa Kagyu clergy and began to garner support among the local populace while continuing to openly defy his rivals in Tibet, including the Tsangpa dynasty. As his fame and popularity grew, "he acquired the sobriquet ‘Zhabdrung Rinpoche’, literally ‘the precious jewel at whose feet one submits’." His growing influence angered not only his Tibetan enemies, but also several powerful rival Buddhist schools of western Bhutan such as the Lhapa sect. Eventually, the Tsangpa invaded Bhutan in collaboration with the Lhapa hierarchs to eliminate Ngawang Namgyal in 1619. This first invasion was eventually defeated by the Bhutanese chieftains who had rallied to Zhabdrung's support, but the conflict between him and the Tsangpa continued, especially since a smallpox epidemic that killed King Karma Phuntsok Namgyal and many other members of the Tibetan dynasty was