Since the beginning of the seventeenth century, the Tokugawa shogunate ruling Japan pursued a policy of isolating the country from outside influences. Foreign trade was maintained only with the Dutch and the Chinese and was conducted exclusively at Nagasaki under a strict government monopoly. No foreigners were allowed to set foot in Japan, and no Japanese was permitted to travel aboard. In June 1635 a law was proclaimed prohibiting the construction of large, ocean-capable vessels. However, by the early nineteenth century, this policy of isolation was increasingly under challenge. In 1844, King William II of the Netherlands sent a letter urging Japan to end the isolation policy on its own before change would be forced from the outside.