Sakashitamon Incident

Sakashitamon Incident (坂下門外の変) was an attack that took place on 13 February 1862 (the 2nd year of Bunkyū) outside Sakashita Gate of Edo Castle, in which six ronin of the Mito Domain who supported Sonnō jōi attacked the Rōjū Andō Nobumasa and wounded him.

Background

After Ii Naosuke, the Tairō, was assassinated in the Sakuradamon Incident, Andō Nobumasa, who together with Kuze Hirochika, the Rōjū, led the shogunate, inherited Naosuke's policy of opening the country and, in order to restore the authority of the shogunate, pursued Kōbu gattai. Under this policy, the shogunate decided to arrange a marriage between Kazunomiya Chikako, the younger sister of the Emperor, and the shogun. However, activists who supported Sonnō jōi opposed this and grew angry at Nobumasa and others.

In July 1860, the first year of Manen, Saimaru Tatemaki, Nomura Tsunenosuke, Sumiya Toranosuke and others of the Mito Domain and Katsura Kogorō, Matsushima Kojō and others of the Chōshū Domain agreed to cooperate and act together (the Heishinmaru Covenant, the Mito–Chōshū Covenant). Accordingly, they planned the assassination of Nobumasa and an attack on foreigners residing in Yokohama. However, within the Chōshū Domain the Kōbu gattai theory of Nagai Uta came to dominate the domain's mainstream, making it difficult for domain retainers to take part. The Chōshū side proposed postponing the plan, but the Mito side, fearing that they would miss their opportunity, decided to carry out the plan independently without Chōshū's support.

The Mito activists, in coordination with the Confucian scholar Ohashi Tōsha and his faction of Utsunomiya Domain, proceeded with the plan to assassinate Nobumasa. Initially it was scheduled to be carried out on 15 December, but for various reasons it was postponed to 28 December, and then again to 15 January. The reason they aimed for that time was that on the day of the (上元) ceremonial rites, many entered the castle and paid their respects to the shogun. However, on 12 January, just before the attack, Ohashi Tōsha and other participants from Utsunomiya were arrested by the shogunate after part of the plan was revealed. Therefore, they could not proceed according to the original plan, and the attack was carried out by the remaining members centered on the Mito activists.