Inside the Satsuma-Chōshū Alliance: What Kido Saw From the Chōshū Side

On January 21, 1866 (the twenty-first of the first month of Keiō 2), at the residence of the Satsuma karō Komatsu Tatewaki in Kyoto, a six-article compact was exchanged between Komatsu and Saigō Takamori on the Satsuma side and Katsura Kogorō (the future Kido Takayoshi) on the Chōshū side. This is the Satsuma-Chōshū Alliance. Without it, neither the Restoration of Imperial Rule the following year nor the Boshin War victory of the anti-bakufu coalition the year after would have happened. One evening that produced the decisive political foundation of the entire late-Bakumatsu turn.

Why Satsuma and Chōshū Were Hard to Reconcile

Satsuma and Chōshū had been in direct combat at the Kinmon Incident in 1864 — Satsuma, in charge of Imperial Palace security, had driven Chōshū's forces out of Kyoto with gunfire. Bitterness ran deep on the Chōshū side. The phrase 'Satsuma the bandit, the Aizu the traitor' was current among Chōshū loyalists. The alliance was not just a strategic agreement; it required two domains that had buried each other's dead two years earlier to politically overwrite that history. For Chōshū-side negotiators including Katsura, the personal stakes were unusually high.

Ryōma's Brokering and Katsura's Silence

The story of the Tosa expatriates Sakamoto Ryōma and Nakaoka Shintarō shuttling between the two domains is well known. Less well advertised is the moment, in the final stage, when Katsura and Saigō were across the table from each other and Katsura stayed silent for about ten days without raising the alliance proposal. Even with Chōshū formally designated an enemy of the Court and in genuinely dire straits, Katsura would not let the encounter take the form of Chōshū petitioning Satsuma for help. Eventually it was Ryōma, reading Katsura's mood, who prompted Saigō to make the opening. The Kido diary records the hesitation in compressed terms.

The Six Articles

The text was a six-article agreement. First: in the event of war between Chōshū and the bakufu, Satsuma would provide rear support. Second: should Chōshū win, Satsuma would work in Kyoto to obtain pardon for Chōshū. Third: should Chōshū lose, Satsuma would defend Chōshū's position at Court. And so on. Formally it was not a military alliance; it was a political coordination pact centered on the Kyoto Court. Substantively, however, those six articles defined the political framework of the entire two-year war that followed. Sakamoto Ryōma wrote an endorsement on the back of the document and handed it to Katsura. That endorsement survives, fixing the moment historically.

"The six articles of the pact, I have understood and received with certainty."