Question: When did the conquest of the region thatY iu Yung-chin claimed the Ming did not possess reach its peak?

full_context: Document 1: Sino-Tibetan relations during the Ming dynasty: Discussions of strategy in the mid Ming dynasty focused primarily on recovery of the Ordos region, which the Mongols used as a rallying base to stage raids into Ming China. Norbu states that the Ming dynasty, preoccupied with the Mongol threat to the north, could not spare additional armed forces to enforce or back up their claim of sovereignty over Tibet; instead, they relied on "Confucian instruments of tribute relations" of heaping unlimited number of titles and gifts on Tibetan lamas through acts of diplomacy. Sperling states that the delicate relationship between the Ming and Tibet was "the last time a united China had to deal with an independent Tibet," that there was a potential for armed conflict at their borders, and that the ultimate goal of Ming foreign policy with Tibet was not subjugation but "avoidance of any kind of Tibetan threat." P. Christiaan Klieger argues that the Ming court's patronage of high Tibetan lamas "was designed to help stabilize border regions and protect trade routes."
Document 2: Sino-Tibetan relations during the Ming dynasty: Historians Luciano Petech and Sato Hisashi argue that the Ming upheld a "divide-and-rule" policy towards a weak and politically fragmented Tibet after the Sakya regime had fallen. Chan writes that this was perhaps the calculated strategy of the Yongle Emperor, as exclusive patronage to one Tibetan sect would have given it too much regional power. Sperling finds no textual evidence in either Chinese or Tibetan sources to support this thesis of Petech and Hisashi. Norbu asserts that their thesis is largely based on the list of Ming titles conferred on Tibetan lamas rather than "comparative analysis of developments in China and Tibet." Rossabi states that this theory "attributes too much influence to the Chinese," pointing out that Tibet was already politically divided when the Ming dynasty began. Rossabi also discounts the "divide-and-rule" theory on the grounds of the Yongle Emperor's failed attempt to build a strong relationship with the fifth Karmapa—one which he hoped would parallel Kublai Khan's earlier relationship with the Sakya Phagpa lama. Instead, the Yongle Emperor followed the Karmapa's advice of giving patronage to many different Tibetan lamas.
Document 3: Sino-Tibetan relations during the Ming dynasty: The official position of the Ministry of Foreign Affairs of the People's Republic of China is that the Ming implemented a policy of managing Tibet according to conventions and customs, granting titles and setting up administrative organs over Tibet. The State Council Information Office of the People's Republic states that the Ming dynasty's Ü-Tsang Commanding Office governed most areas of Tibet. It also states that while the Ming abolished the policy council set up by the Mongol Yuan to manage local affairs in Tibet and the Mongol system of Imperial Tutors to govern religious affairs, the Ming adopted a policy of bestowing titles upon religious leaders who had submitted to the Ming dynasty. For example, an edict of the Hongwu Emperor in 1373 appointed the Tibetan leader Choskunskyabs as the General of the Ngari Military and Civil Wanhu Office, stating:
Document 4: Sino-Tibetan relations during the Ming dynasty: The late Turrell V. Wylie, a former professor of the University of Washington, and Li Tieh-tseng argue that the reliability of the heavily censored History of Ming as a credible source on Sino-Tibetan relations is questionable, in the light of modern scholarship. Other historians also assert that these Ming titles were nominal and did not actually confer the authority that the earlier Yuan titles had. Van Praag writes that the "numerous economically motivated Tibetan missions to the Ming Court are referred to as 'tributary missions' in the Ming Shih." Van Praag writes that these "tributary missions" were simply prompted by China's need for horses from Tibet, since a viable horse market in Mongol lands was closed as a result of incessant conflict. Morris Rossabi also writes that "Tibet, which had extensive contacts with China during the Yuan, scarcely had diplomatic relations with the Ming."
Document 5: Sino-Tibetan relations during the Ming dynasty: Laird writes that Altan Khan abolished the native Mongol practices of shamanism and blood sacrifice, while the Mongol princes and subjects were coerced by Altan to convert to Gelug Buddhism—or face execution if they persisted in their shamanistic ways. Committed to their religious leader, Mongol princes began requesting the Dalai Lama to bestow titles on them, which demonstrated "the unique fusion of religious and political power" wielded by the Dalai Lama, as Laird writes. Kolmaš states that the spiritual and secular Mongol-Tibetan alliance of the 13th century was renewed by this alliance constructed by Altan Khan and Sönam Gyatso. Van Praag writes that this restored the original Mongol patronage of a Tibetan lama and "to this day, Mongolians are among the most devout followers of the Gelugpa and the Dalai Lama." Angela F. Howard writes that this unique relationship not only provided the Dalai Lama and Panchen Lama with religious and political authority in Tibet, but that Altan Khan gained "enormous power among the entire Mongol population."
Document 6: Sino-Tibetan relations during the Ming dynasty: Dawa Norbu argues that modern Chinese Communist historians tend to be in favor of the view that the Ming simply reappointed old Yuan dynasty officials in Tibet and perpetuated their rule of Tibet in this manner. Norbu writes that, although this would have been true for the eastern Tibetan regions of Amdo and Kham's "tribute-cum-trade" relations with the Ming, it was untrue if applied to the western Tibetan regions of Ü-Tsang and Ngari. After the Phagmodrupa Changchub Gyaltsen, these were ruled by "three successive nationalistic regimes," which Norbu writes "Communist historians prefer to ignore."
Document 7: Sino-Tibetan relations during the Ming dynasty: The Ming initiated sporadic armed intervention in Tibet during the 14th century, but did not garrison permanent troops there. At times the Tibetans also used armed resistance against Ming forays. The Wanli Emperor (r. 1572–1620) made attempts to reestablish Sino-Tibetan relations after the Mongol-Tibetan alliance initiated in 1578, which affected the foreign policy of the subsequent Qing dynasty (1644–1912) of China in their support for the Dalai Lama of the Gelug school. By the late 16th century, the Mongols were successful armed protectors of the Gelug Dalai Lama, after increasing their presence in the Amdo region. This culminated in Güshi Khan's (1582–1655) conquest of Tibet from 1637–1642 and the establishment of the Ganden Phodrang regime by the 5th Dalai Lama with his help.
Document 8: Sino-Tibetan relations during the Ming dynasty: Laird writes that the Ming appointed titles to eastern Tibetan princes, and that "these alliances with eastern Tibetan principalities are the evidence China now produces for its assertion that the Ming ruled Tibet," despite the fact that the Ming did not send an army to replace the Mongols after they left Tibet. Yiu Yung-chin states that the furthest western extent of the Ming dynasty's territory was Gansu, Sichuan, and Yunnan while "the Ming did not possess Tibet."
Document 9: Sino-Tibetan relations during the Ming dynasty: Kolmaš writes that, as the Mongol presence in Tibet increased, culminating in the conquest of Tibet by a Mongol leader in 1642, the Ming emperors "viewed with apparent unconcern these developments in Tibet." He adds that the Ming court's lack of concern for Tibet was one of the reasons why the Mongols pounced on the chance to reclaim their old vassal of Tibet and "fill once more the political vacuum in that country." On the mass Mongol conversion to Tibetan Buddhism under Altan Khan, Laird writes that "the Chinese watched these developments with interest, though few Chinese ever became devout Tibetan Buddhists."
Document 10: Sino-Tibetan relations during the Ming dynasty: Nevertheless, the ethno-geographic caste hierarchy favoring the Mongols and other ethnicities were accorded higher status than the Han Chinese majority. Although Han Chinese who were recruited as advisers were often actually more influential than high officials, their status was not as well defined. Kublai also abolished the imperial examinations of China's civil service legacy, which was not reinstated until Ayurbarwada Buyantu Khan's reign (1311–1320). Rossabi writes that Kublai recognized that in order to rule China, "he had to employ Chinese advisors and officials, yet he could not rely totally on Chinese advisers because he had to maintain a delicate balancing act between ruling the sedentary civilization of China and preserving the cultural identity and values of the Mongols." And "in governing China, he was concerned with the interests of his Chinese subjects, but also with exploiting the resources of the empire for his own aggrandizement. His motivations and objectives alternated from one to the other throughout his reign," according to Rossabi. Van Praag writes in The Status of Tibet that the Tibetans and Mongols, on the other hand, upheld a dual system of rule and an interdependent relationship that legitimated the succession of Mongol khans as universal Buddhist rulers, or chakravartin. Van Praag writes that "Tibet remained a unique part of the Empire and was never fully integrated into it," citing examples such as a licensed border market that existed between China and Tibet during the Yuan.
Document 11: Sino-Tibetan relations during the Ming dynasty: Patricia Ebrey writes that Tibet, like Joseon Korea and other neighboring states to the Ming, settled for its tributary status while there were no troops or governors of Ming China stationed in its territory. Laird writes that "after the Mongol troops left Tibet, no Ming troops replaced them." Wang and Nyima state that, despite the fact that the Ming refrained from sending troops to subdue Tibet and refrained from garrisoning Ming troops there, these measures were unnecessary so long as the Ming court upheld close ties with Tibetan vassals and their forces. However, there were instances in the 14th century when the Hongwu Emperor did use military force to quell unrest in Tibet. John D. Langlois writes that there was unrest in Tibet and western Sichuan, which the Marquis Mu Ying (沐英) was commissioned to quell in November 1378 after he established a Taozhou garrison in Gansu. Langlois notes that by October 1379, Mu Ying had allegedly captured 30,000 Tibetan prisoners and 200,000 domesticated animals. Yet invasion went both ways; the Ming general Qu Neng, under the command of Lan Yu, was ordered to repel a Tibetan assault into Sichuan in 1390.
Document 12: Sino-Tibetan relations during the Ming dynasty: Shih-Shan Henry Tsai writes that the Yongle Emperor sent his eunuch Yang Sanbao into Tibet in 1413 to gain the allegiance of various Tibetan princes, while the Yongle Emperor paid a small fortune in return gifts for tributes in order to maintain the loyalty of neighboring vassal states such as Nepal and Tibet. However, Van Praag states that Tibetan rulers upheld their own separate relations with the kingdoms of Nepal and Kashmir, and at times "engaged in armed confrontation with them."
Document 13: Sino-Tibetan relations during the Ming dynasty: Helmut Hoffman states that the Ming upheld the facade of rule over Tibet through periodic missions of "tribute emissaries" to the Ming court and by granting nominal titles to ruling lamas, but did not actually interfere in Tibetan governance. Melvyn C. Goldstein writes that the Ming had no real administrative authority over Tibet, as the various titles given to Tibetan leaders did not confer authority as the earlier Mongol Yuan titles had. He asserts that "by conferring titles on Tibetans already in power, the Ming emperors merely recognized political reality." Hugh Edward Richardson writes that the Ming dynasty exercised no authority over the succession of Tibetan ruling families, the Phagmodru (1354–1435), Rinpungpa (1435–1565), and Tsangpa (1565–1642).
Document 14: Sino-Tibetan relations during the Ming dynasty: With the example of the Ming court's relationship with the fifth Karmapa and other Tibetan leaders, Norbu states that Chinese Communist historians have failed to realize the significance of the religious aspect of the Ming-Tibetan relationship. He writes that the meetings of lamas with the Emperor of China were exchanges of tribute between "the patron and the priest" and were not merely instances of a political subordinate paying tribute to a superior. He also notes that the items of tribute were Buddhist artifacts which symbolized "the religious nature of the relationship." Josef Kolmaš writes that the Ming dynasty did not exercise any direct political control over Tibet, content with their tribute relations that were "almost entirely of a religious character." Patricia Ann Berger writes that the Yongle Emperor's courting and granting of titles to lamas was his attempt to "resurrect the relationship between China and Tibet established earlier by the Yuan dynastic founder Khubilai Khan and his guru Phagpa." She also writes that the later Qing emperors and their Mongol associates viewed the Yongle Emperor's relationship with Tibet as "part of a chain of reincarnation that saw this Han Chinese emperor as yet another emanation of Manjusri."
Document 15: Sino-Tibetan relations during the Ming dynasty: Wang and Nyima argue that the Ming emperor sent edicts to Tibet twice in the second year of the Ming dynasty, and demonstrated that he viewed Tibet as a significant region to pacify by urging various Tibetan tribes to submit to the authority of the Ming court. They note that at the same time, the Mongol Prince Punala, who had inherited his position as ruler of areas of Tibet, went to Nanjing in 1371 to pay tribute and show his allegiance to the Ming court, bringing with him the seal of authority issued by the Yuan court. They also state that since successors of lamas granted the title of "prince" had to travel to the Ming court to renew this title, and since lamas called themselves princes, the Ming court therefore had "full sovereignty over Tibet." They state that the Ming dynasty, by issuing imperial edicts to invite ex-Yuan officials to the court for official positions in the early years of its founding, won submission from ex-Yuan religious and administrative leaders in the Tibetan areas, and thereby incorporated Tibetan areas into the rule of the Ming court. Thus, they conclude, the Ming court won the power to rule Tibetan areas formerly under the rule of the Yuan dynasty.
ground_truth: 1642
sub_queries: What does Yiu Yung-chin claim the Ming did not possess? Answer: Tibet
When did the conquest of Tibet reach its peak? Answer: 1642