Noting the strategic/military danger it would present to Japan if a Western power were to gain control of Korea, and thinking Qing Dynasty China particularly weak in the aftermath of the 1860 Anglo-French occupation of Beijing and the still ongoing Taiping Rebellion, Yamada was in 1861-1862 advocating a Japanese invasion of not only Korea, but also of China and Taiwan, to take advantage of China's weakness, and by seizing this land away from the Westerners, to better secure the defense of Japan. In 1861, he suggested the Itakura present memorials to that effect to the shogunate, proposing that Satsuma and Chôshû forces, along with shogunate-owned warships, be used to launch a three-pronged attack against China, Korea, and Taiwan. He believed that the Japanese could win "the hearts and minds" of the people of these regions by ruling righteously, restoring the region to the golden age of the Tang Dynasty.
Yamada was introduced by Kido Takayoshi of Chôshû to Ôshima Tomonojô of Tsushima han in early 1863, and had an influence upon both men, who thereafter leaned a bit more towards advocating, or supporting, an invasion of Korea.
- Robert Hellyer, Defining Engagement, Harvard University Press (2009), 220.