from these regions, which were then incorporated into the empire. Galdan was eventually killed in the Dzungar–Qing War. In 1683, Qing forces received the surrender of Formosa (Taiwan) from Zheng Keshuang, grandson of Koxinga, who had conquered Taiwan from the Dutch colonists as a base against the Qing. Winning Taiwan freed Kangxi's forces for a series of battles over Albazin, the far eastern outpost of the Tsardom of Russia. The 1689 Treaty of Nerchinsk was China's first formal treaty with a European power and kept the border peaceful for the better part of two centuries. After Galdan's death, his followers, as adherents to Tibetan Buddhism, attempted to control the choice of the next Dalai Lama. Kangxi dispatched two armies to Lhasa, the capital of Tibet, and installed a Dalai Lama sympathetic to the Qing. Reigns of the Yongzheng and Qianlong emperors The reigns of the Yongzheng Emperor (r. 1723–1735) and his son, the Qianlong Emperor (r. 1735–1796), marked the height of Qing power. Yet, as the historian Jonathan Spence puts it, the empire by the end of the Qianlong reign was "like the sun at midday". In the midst of "many glories", he writes, "signs of decay and even collapse were becoming apparent". After the death of the Kangxi Emperor in the winter of 1722, his fourth son, Prince Yong (), became the Yongzheng Emperor. In the later years of Kangxi's reign, Yongzheng and his brothers had fought, and there were unsubstantiated rumors that he had usurped the throne by tampering with the Kangxi's testament on the night when Kangxi died. In fact, his father had trusted him with delicate political issues and discussed state policy with him. When Yongzheng came to power at the age of 45, he felt a sense of urgency about the problems that had accumulated in his father's later years, and he did not need instruction on how to exercise power. In the words of one recent historian, he was "severe, suspicious, and jealous, but extremely capable and resourceful", and in the words of another, he turned out to be an "early modern state-maker of the first order". Yongzheng moved rapidly. First, he promoted Confucian orthodoxy and reversed what he saw as his father's laxness by cracking down on unorthodox sects and by decapitating an anti-Manchu writer his father had pardoned. In 1723 he outlawed Christianity and expelled Christian missionaries, though some were allowed to