[1] He 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.

[7] While an attack at the front drew the attention of the guards, a lone assassin fired one shot into the palanquin containing Ii, with a Japanese-made Colt 1851 Navy Revolver, which had been copied from the firearms that Commodore Matthew Perry had given the shogunate as gifts.

Therefore, we have consecrated ourselves to be the instruments of Heaven to punish this wicked man, and we have taken on ourselves the duty of ending a serious evil, by killing this atrocious autocrat.Accounts of the violent event were sent via ship across the Pacific to San Francisco and then sped by the Pony Express across the American West.

[10] The assassination dealt a severe blow to the prestige of the shogunate such that officials refused to admit Naosuke's death for a month, claiming that he was merely injured and was recuperating.

According to Sir Ernest Satow: "A bloody revenge was taken on the individual [Ii], but the hostility to the system only increased with time, and in the end brought about its complete ruin".

Despite the defeat of the Bakufu, the new government adopted a policy of trade and diplomatic relations with the Western powers closer to that of Ii Naosuke than that of his assassins.