Satsuma-Chōshū Alliance

On January 21, Keiō 2 (1866), at the Konoe family's Kyōto residence known as the Ohanabatake Mansion (the residence of Kommatsu Taisaku), representatives of the Satsuma and Chōshū domains concluded a secret military agreement. This "Satsuma-Chōshū Alliance" (also called the Satsuma-Chōshū Covenant or Satsuma-Chōshū Union), realized through the persistent mediation of Sakamoto Ryōma and Nakaoka Shintarō, became the foundation for the overthrow of the Edo shogunate and the Meiji Restoration. It remains one of the most dramatic and influential political alliances in Japanese history, spoken of to this day.

From Confrontation to Cooperation: The Long Conflict between Satsuma and Chōshū

The Satsuma and Chōshū domains had been in intense conflict during the early bakumatsu period. In August of Bunkyu 3 (1863), the "August 18 Coup" saw the Satsuma and Aizu domains join forces to expel Chōshū forces from Kyōto. The following year, in July of Genji 1 (1864), the "Kinmon Incident" saw combined forces of Satsuma, Aizu, and Kuwana repel Chōshū's attack on the Imperial Palace. Chōshū was branded an "enemy of the court," and the First Chōshū Expedition forced it into submission, with Satsuma's participation in the campaign playing a major role.

However, both Satsuma and Chōshū had experienced the Satsuma-British War (Bunkyu 3, 1863) and the Shimonoseki War (Genji 1, 1864) respectively, deepening their understanding of Western military power and painfully recognizing the importance of Western-style weapons and training. Discontent with the shogunate's diplomatic policy of opening the country and free trade, combined with the ideological shift from "revere the emperor and expel the barbarians" to "armed overthrow of the shogunate," was creating the conditions for both domains' interests to align.

The Mediation of Sakamoto Ryōma and Nakaoka Shintarō

The role of bridge between Satsuma and Chōshū fell to Sakamoto Ryōma and Nakaoka Shintarō, both Tosa rōnin. Ryōma studied Western-style naval science under the shogunate official Katsu Kaishū, and subsequently established the Kameyama Shachu (later the Kaientai) in Nagasaki, engaging in shipping and the arms trade. With his broad network of connections among the Satsuma, Chōshū, Tosa, and restoration activists throughout the country, he conducted mediation efforts from a unique position unconstrained by any particular domain or ideology.

Nakaoka Shintarō was a Tosa-domain rōnin who organized the Rikuentai and devoted himself to the anti-shogunate movement, maintaining especially deep connections with Katsura Kogorō (Kido Takayoshi) of Chōshū. Ryōma primarily handled the approach to the Satsuma side (Saigō Takamori and Kommatsu Taisaku), while Nakaoka handled the approach to the Chōshū side (Katsura Kogorō), advancing the mediation in this division of labor.

From autumn through winter of Keiō 1 (1865), Ryōma worked tirelessly to link Chōshū's weapons and supplies problems with Satsuma's political interests. Chōshū needed Western-style weapons (Minié rifles) for rearmament after the First Expedition, and Satsuma was able to procure weapons through the British merchant Glover. Ryōma mediated a transaction in which Satsuma would purchase weapons on behalf of Chōshū, thus binding the two domains' interests together in practical terms.

The Conclusion of the Alliance: The Secret Covenant at Kommatsu Taisaku's Residence

From January 14, Keiō 2 (1866), for several days, Ryōma and Nakaoka, together with Chōshū representative Katsura Kogorō, gathered in Kyōto and conducted negotiations with Satsuma representatives Saigō Takamori and Kommatsu Taisaku. Due to years of conflict and mutual distrust, Katsura Kogorō remained suspicious of Satsuma's sincerity until the end, making negotiations difficult. Ryōma mediated between them, continuing his persuasion through the night.

On January 21 (old calendar; March 7 by the new calendar), at last agreement was reached at Kommatsu Taisaku's residence. The content of the covenant became known through the "Kido Documents," a record kept by Katsura Kogorō himself. The principal articles were as follows:

First, should the shogunate begin war against Chōshū, Satsuma shall immediately dispatch troops to the Kyōto-Ōsaka region and fight against the shogunate forces.

Second, should the shogunate army attack Chōshū, Satsuma shall provide support to Chōshū.

Third, once Chōshū is cleared of the stigma of being an "enemy of the court" and formally pardoned by the imperial court, Satsuma and Chōshū shall cooperate together for the good of the nation.

Ryōma witnessed this covenant and, in response to Katsura Kogorō's concerns, is said to have served as guarantor, declaring, "Should Satsuma break its promise, I shall apologize with my life."

The Second Chōshū Expedition and the Proof of the Alliance

Only a few months after the Satsuma-Chōshū Alliance was concluded, the shogunate launched the Second Chōshū Expedition (June 1866 onward). This time Chōshū mounted direct military resistance, and Satsuma maintained neutrality, refusing to participate in the shogunate forces. As a result, the Second Expedition, fought on four fronts—Sekishū, Ōshima, Kokura, and Geishū—saw the Chōshū forces centered on the Kiheitai repel and overwhelm the shogunate army, resulting in a shogunate defeat. The death of Shogun Tokugawa Iemochi at Ōsaka Castle (August 20, 1866) compounded matters, forcing the shogunate to abandon the campaign.

This defeat decisively undermined the shogunate's military authority, and the anti-shogunate movement rapidly emerged as a practical option. The Satsuma-Chōshū Alliance functioned as the core of the anti-shogunate forces in the following year, Keiō 3 (1867), during the Taisei Hōkan (return of political authority) and the Ōsei Fukko no Daigōrei (Restoration of Imperial Rule), and in the following Keiō 4 (1868) during the Boshin War and the Toba-Fushimi Battle.

Swords and the Change of the Bakumatsu: What the Satsuma-Chōshū Alliance Symbolizes

The Satsuma-Chōshū Alliance holds important meaning also from the perspective of bakumatsu sword culture. Throughout the Edo period, the Japanese sword, regarded as the "soul of the warrior," continued to symbolize samurai identity even in the bakumatsu. Katsura Kogorō, Saigō Takamori, Sakamoto Ryōma, and the other protagonists of the covenant were all samurai who wore both long and short swords, and the Satsuma-Chōshū Alliance was quite literally a political covenant agreed upon by sword-bearing warriors.

Yet the core of the covenant lay in military transformation toward Western-style rifle units and the Kiheitai. The weapons support provided by Satsuma to Chōshū (Western-style rifles such as Minié guns) and the new military system established by Chōshū through Takasugi Shinsaku and the Kiheitai represented a shift toward a military system centered on modern weapons that removed the Japanese sword from its role as the primary weapon on the battlefield. The Satsuma-Chōshū Alliance was also an event that institutionally and militarily prepared "the beginning of the end of the age of the samurai."

Sakamoto Ryōma was assassinated at the Ōmi-ya in Kyōto on November 15, Keiō 3 (1867), the year following the conclusion of the Satsuma-Chōshū Alliance. The Satsuma-Chōshū Alliance, which he realized by staking his life, formed the foundation of the post-Restoration Meiji government and determined Japan's modernization. In this sense, the Satsuma-Chōshū Alliance, as a nexus in history where samurai bearing swords opened a new era, remains forever in Japanese history.