薩長同盟
After radical elements under Takasugi Shinsaku gained control of Chōshū politics, Katsura, under the new name was instrumental in establishing the Satchō Alliance with Saigō Takamori and Ōkubo Toshimichi through the mediation of Sakamoto Ryōma in 1866, which proved to be critical in the Boshin War and the subsequent Meiji Restoration. Around the same time, he adopted Shojirō, another nephew who was the second son of his younger sister, Kuribara Haruko, as his heir.