and forced the shōgun to sign the "Treaty of Peace and Amity", establishing formal diplomatic relations between Japan and the United States, known as the Convention of Kanagawa (March 31, 1854). Within five years Japan had signed similar treaties with other western countries. The Harris Treaty was signed with the United States on July 29, 1858. These treaties were widely regarded by Japanese intellectuals as unequal, having been forced on Japan through gunboat diplomacy, and as a sign of the West's desire to incorporate Japan into the imperialism that had been taking hold of the continent. Among other measures, they gave the Western nations unequivocal control of tariffs on imports and the right of extraterritoriality to all their visiting nationals. They would remain a sticking point in Japan's relations with the West up to the start of the 20th century. Modernization: Bakumatsu period (1853–1868) The study of Western shipbuilding techniques resumed in the 1840s. This process intensified along with the increased activity of Western shipping along the coasts of Japan, due to the China trade and the development of whaling. From 1852, the government of the shōgun (the Late Tokugawa shogunate or "Bakumatsu") was warned by the Netherlands of the plans of Commodore Perry. Three months after Perry's first visit in 1853, the Bakufu cancelled the law prohibiting the construction of large ships (大船建造禁止令), and started organizing the construction of a fleet of Western-style sail warships, such as the Hōō Maru, the Shōhei Maru or the Asahi Maru, usually asking each fief to build their own modern ships. These ships were built using Dutch sailing manuals, and the know-how of a few returnees from the West, such as Nakahama Manjirō. Also with the help of Nakahama Manjirō, the Satsuma fief built Japan's first steam ship, the Unkoumaru (雲行丸) in 1855. The Bakufu also established defensive coastal fortifications, such as at Odaiba. Birth of a modern navy As soon as Japan agreed to open up to foreign influence, the Tokugawa shōgun government initiated an active policy of assimilation of Western naval technologies. In 1855, with Dutch assistance, the shogunate acquired its first steam warship, the Kankō Maru, which was used for training, and established the Nagasaki Naval Training Center. In 1857, it acquired its first screw-driven steam warship, the Kanrin Maru. In 1860, the Kanrin Maru was sailed to the United States by a group of Japanese, with the assistance of