Task: Question Generation
Input (English): Elliot Sperling, a specialist of Indian studies and the director of the Tibetan Studies program at Indiana University’s Department of Central Eurasia Studies, writes that "the idea that Tibet became part of China in the 13th century is a very recent construction." He writes that Chinese writers of the early 20th century were of the view that Tibet was not annexed by China until the Manchu Qing dynasty invasion during the 18th century. He also states that Chinese writers of the early 20th century described Tibet as a feudal dependency of China, not an integral part of it. Sperling states that this is because "Tibet was ruled as such, within the empires of the Mongols and the Manchus" and also that "China's intervening Ming dynasty ... had no control over Tibet." He writes that the Ming relationship with Tibet is problematic for China’s insistence of its unbroken sovereignty over Tibet since the 13th century. As for the Tibetan view that Tibet was never subject to the rule of the Yuan or Qing emperors of China, Sperling also discounts this by stating that Tibet was "subject to rules, laws and decisions made by the Yuan and Qing rulers" and that even Tibetans described themselves as subjects of these emperors.
Output (English): Since what century has Sperling described Ming and Tibet's relation being problematic for China?