percentage of the population (1%) in Japan remains far lower than in other East Asian countries such as China (3%), Vietnam (7%) and South Korea (29%). The policy was also a way of controlling commerce between Japan and other nations, as well as asserting its new place in the East Asian hierarchy. The Tokugawa had set out to create their own small-scale international system where Japan could continue to access the trade in essential commodities such as medicines, and gain access to essential intelligence about happenings in China while avoiding having to agree to a subordinate status within the Chinese tributary system. Japan's generally constructive official diplomatic relationship with Joseon Korea allowed regular embassies (Tongsinsa) to be dispatched by Korea to Japan. Together with the brisk trade between Tsushima and Korea, as well as the presence of Japanese in the Busan wakan, Japan was able to access Chinese cultural, intellectual and technological developments throughout the Edo period. At the time of the promulgation of the strictest versions of the maritime prohibitions, the Ming dynasty had lost control of much of China and it was unnecessary, and perhaps undesirable, for Japan to pursue official diplomatic relations with either of the Ming or the Qing governments while the issue of imperial legitimacy was unsettled. Japan was able to acquire the imported goods it required through intermediary trade with the Dutch and through the Ryukyu Islands. The Japanese actually encouraged the Ryūkyū Kingdom's rulers to maintain a tributary relationship with China, even though the Shimazu clan had surreptitiously established great political influence in the Ryukyu Islands. The Qing became much more open to trade after it had defeated the Ming loyalists in Taiwan, and thus Japan's rulers felt even less need to establish official relations with China. Liberalizing challenges to came from within Japan's elite in the 18th century, but they came to nothing. Later on, the policy was the main safeguard against the total depletion of Japanese mineral resources—such as silver and copper—to the outside world. However, while silver exportation through Nagasaki was controlled by the shogunate to the point of stopping all exportation, the exportation of silver through Korea continued in relatively high quantities. The way Japan kept abreast of Western technology during this period was by studying medical and other texts in the Dutch language obtained through Dejima. This developed into a blossoming field in the late 18th century which