Further, under intense pressure from America, Britain and France, Ii took the unprecedented step of acting without the consent of the Emperor, an exclusionist, and signed the Harris Treaty with the U.S. He opened Yokohama for foreign trade, and sent a Japanese ambassador to Washington. Opposition was executed, imprisoned or exiled, including Nariaki, who was placed under house arrest.
The insult to the Emperor and to the house of Mito could not, in traditional Japan, pass unavenged. Ii was assassinated at the Sakurada Gate of Edo Castle on a snowy morning in March, 1860, as he arrived in a palanquin(background left) to attend the Shogun's court. His assassins, seventeen Mito and Satsuma samurai, waited near the gate with swords hidden under snow capes. Despite the print, they surprised Ii's bodyguard, killing Ii in the palaquin, before he could react.
Although the exclusionists were back in power, Nariaki died in September the same year. And, it was already too late. The treaties were signed: Japan could not easily reverse direction.