On March 31, 1854, the Convention of Kanagawa (Japanese:神奈川条約,or 日米和親条約) was used by Commodore Matthew Perry of the U.S. Navy to force the opening of the Japanese ports of Shimoda and Hakodate to American trade and ended Japan's 200 year policy of seclusion. It also guaranteed safety of shipwrecked American whalers and established a permanent American consul. Though he refused to deal with Japanese officials and demanded to speak with the Japanese Head of State, Perry did not realize that he had only spoken with representatives of the Tokugawa Shogun and not the Emperor. However, the Shogun was the de-facto ruler of Japan at that time. For the Emperor to interact in any way with foreigners was out of the question. After the Treaty of Kanagawa was concluded, similar treaties were negotiated by the Russians and the British.
See History of Japan.
Full text of the treaty can be found here.
See also The Treaty of Amity and Commerce Between the United States and Japan, 1858 (The Harris Treaty).