Second Battle of Simtokha Dzong
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 attributed to Ngawang Namgyal's alleged magical powers.
After a time of self-chosen seclusion, Zhabdrung proclaimed his intention to become the spiritual and temporal ruler of Bhutan. While the Drukpa Kagyu, Sakya, and Nyingma schools as well as many chieftains accepted his political domination, several other lamas did not and continued to resist him. As he consolidated his control over the western valleys, Zhabdrung began to construct a strategically placed dzong as his seat of power in 1629. It was during the construction that five lamaist factions attacked his party and his supporters. The following First Battle of Simtokha Dzong resulted in a decisive victory of Ngawang Namgyal's forces, while the dzong was finished in 1631. 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. For some years, however, negotiations between the Tibetans and Ngawang Namgyal's followers took place to avoid war. These proved unfruitful, and as result the Tsangpa launched their second invasion in 1634. This led the Bhutanese to claim that the Tibetan ruler had never wanted peace and that the negotiations had been a mere strategic ploy. King Karma Tenkyong's exact motives for the invasion remain unclear, however, with Karma Phuntsho speculating that he either wanted to capture Zhabdrung, destabilize his rule in Bhutan, or obtain revered Tibetan relics that were in Bhutanese possession. In any case, the new invasion appears to have been much larger and better prepared than the one of 1619.