The Black Ships (in 黒船, Edo period term) was the name given to Western vessels arriving in Japan in the 16th and 19th centuries. In 1543 Portuguese initiated the first contacts, establishing a trade route linking Goa to Nagasaki. The large carracks engaged in this trade had the hull painted black with pitch, and the term came to represent all Western vessels. In 1639, after suppressing a rebellion blamed on the influence of Christian thought, the ruling Tokugawa shogunate retreated into an isolationist policy, the Sakoku. During this "locked state", contact with Japan by Westerners was restricted to Dejima island at Nagasaki. In 1844, William II of the Netherlands urged Japan to open, but was rejected. On July 8, 1853, the U.S. Navy sent four warships into the bay at Edo and threatened to attack if Japan did not begin trade with the West. Their arrival marked the reopening of the country to political dialogue after more than two hundred years of self-imposed isolation. Trade with Western nations would not come until the Treaty of Amity and Commerce more than five years later. In particular, kurofune refers to Mississippi, Plymouth, Saratoga, and Susquehanna of the Perry Expedition for the opening of Japan, 1852–1854, that arrived on July 14, 1853, at Uraga Harbor (part of present-day Yokosuka) in Kanagawa Prefecture, Japan under the command of United States Commodore Matthew Perry. Black refers to the black color of the older sailing vessels, and the black smoke from the coal-fired steam engines of the American ships. In this sense, the kurofune became a symbol of the ending of isolation. In 1543 Portuguese traders arrived in Japan initiating the first contacts with the West. Soon they established a trade route linking their headquarters in Goa, via Malacca to Nagasaki. Large carracks engaged in the flourishing "Nanban trade", introducing modern inventions from the European traders, such as refined sugar, optics, and firearms; it was the firearms, arquebuses, which became a major innovation of the Sengoku period—a time of intense internal warfare—when the matchlocks were replicated.