Sakuradamon Gate Incident
Who would become 14th shogun was the greatest concern in those days.
Mito domain (today's Ibaragi prefecture) recommended Yoshinobu so that they might take the intiative in the government.
But Ii Naosuke supported Iemochi of Ki domain (today's Wakayaa) as the 14th shogun.
In the end Iemochi became the 14th shogun of the Edo government.
Mito groups, completely defeated in the succession of shogun, blamed Ii Naosuke for his diplomatic policy instead. They tried to expel him from the position. They attacked him, saying the Treaty of Amity and Commerce would be invalid because it was not permitted by the emperor.
They made use of the emperor.
It was a taboo in the Edo shogunate to involve emperors in political affairs.
One of the major families in the Edo shogun comitted such a crucial mistake which shook the base of the government. In his eyes, Mito group's activities were equal to anti-government campaign to overthrow the Edo government.
Naosuke arrested anti-foreigner leaders across Japan and punished them to death.
Mito domain which lost leading figures was like a powder magazine.
In early morning in 1860 winter, 18 samurai members selected from the Mito groups attacked and assassinated Naosuke outside the Sakuradamon gate of Edo castle (today's Imperial Palace).
The Edo government lost the key person.
There was no talented person to deal with difficulties and lead the samurai government.