Knowledgeable on naval and coastal defense issues, Shozan was imprisoned by the Tokugawa Bakufu from 1854 to 1862. He advocated opening Japanese ports to foreign traders.
Shōzan was assassinated for his opinions by some radical anti-foreigner groups. The groups hired an assasin, or hitokiri named Kawakami Gensai who felled Shozan with one strike in broad daylight.
One was Sakuma- Shozan, hereditary retainer of one of the Shogun's councillors, and from him he got more than money or than money's worth.
A steady, respectable man, with an eye to the world's opinion, Sakuma was one of those who, if they cannot do great deeds in their own person, have yet an ardour of admiration for those who can, that recommends them to the gratitude of history.
Sakuma, implicated by his handwriting, was sent into his own province in confinement, from which he was soon released.