薩長同盟
When the shogunate decided to finally defeat Chōshū in a Second Chōshū expedition the next year, Satsuma, under the lead of Saigo Takamori and Ōkubo Toshimichi, decided to switch sides. The Satchō Alliance between Satsuma and Chōshū was brokered by Sakamoto Ryōma from Tosa.