P. Christiaan Klieger, an anthropologist and scholar of the California Academy of Sciences in San Francisco, writes that the vice royalty of the Sakya regime installed by the Mongols established a patron and priest relationship between Tibetans and Mongol converts to Tibetan Buddhism. According to him, the Tibetan lamas and Mongol khans upheld a "mutual role of religious prelate and secular patron," respectively. He adds that "Although agreements were made between Tibetan leaders and Mongol khans, Ming and Qing emperors, it was the Republic of China and its Communist successors that assumed the former imperial tributaries and subject states as integral parts of the Chinese nation-state."