Ii, a leading figure of the Bakumatsu period and a proponent of the reopening of Japan after more than 200 years of seclusion, was widely criticized for signing the 1858 Treaty of Amity and Commerce with the United States Consul Townsend Harris and, soon afterwards, similar treaties with other Western countries.
From 1859, the ports of Nagasaki, Hakodate and Yokohama became open to foreign traders as a consequence of the Treaties.

Ii was also criticized for reinforcing the authority of the Tokugawa shogunate against regional daimyōs through the Ansei Purge.
Naosuke also made strong enemies in the dispute for the succession of Shōgun Tokugawa Iesada, and because he forced retirement on his opponents, specifically the retainers of Mito, Hizen, Owari, Tosa, Satsuma and Uwajima.

These policies generated strong sentiment against the Shogunate, especially among proponents of the Mito school.
Ii, a leading figure of the Bakumatsu period and a proponent of the reopening of Japan after more than 200 years of seclusion, was widely criticized for signing the 1858 Treaty of Amity and Commerce with the United States Consul Townsend Harris and, soon afterwards, similar treaties with other Western countries. From 1859, the ports of Nagasaki, Hakodate and Yokohama became open to foreign traders as a consequence of the Treaties.
Ii was also criticized for reinforcing the authority of the Tokugawa shogunate against regional daimyōs through the Ansei Purge. Naosuke also made strong enemies in the dispute for the succession of Shōgun Tokugawa Iesada, and because he forced retirement on his opponents, specifically the retainers of Mito, Hizen, Owari, Tosa, Satsuma and Uwajima.
These policies generated strong sentiment against the Shogunate, especially among proponents of the Mito school.
Sakuradamon Incident (1860)