 The singular importance of the head of the VOC in Japan during this period was enhanced by the Japanese policy of "sakoku"imposed isolation.Because of religious proselytizing by Europeans during the 16th century, the Tokugawa shogunate introduced a policy in the early 17th century that no European or Japanese could enter or leave the Japanese archipelago on penalty of death.The sole exception to this "closed door" was the VOC "factory" (trading post) on the island of Dejima in Nagasaki Bay, on the southern Japanese island of Kyūshū.