From 1842, following an analysis of the defeat of China against Great Britain in the First Opium War and the spread of Western influence in Asia, Sakuma actively proposed the introduction of Western military methods to the Bakufu and the establishment of maritime defense, through his book "Eight policies for the defense of the sea" (). After the Bakufu ordered Japanese translations of the "Military History of the Qing dynasty" (, "Shèngwu Ji") and the "Illustrated Treatise on the Maritime Kingdoms" written by Chinese scholar Wei Yuan (17941857), Sakuma was struck by the similarities in their ideas in defending against the west. His writing brought some fame, and he became the teacher of several future leaders of modernization (Yoshida Shōin, Katsu Kaishū, Sakamoto Ryōma, Nakaoka Shintarō, Hashimoto Sanai, Katō Hiroyuki, Nishimura Shigeki, Yamamoto Kakuma).