They had spent a year nursing their shame. On August 20, 1864, roughly 3,000 Choshu samurai marched on the Kyoto Imperial Palace to take back what had been taken from them without a fight.

The August 18 Coup of 1863 had been elegant in its cruelty: Satsuma and Aizu had sealed all nine palace gates in the pre-dawn dark and stripped Choshu of its honored post at the Sakaimachi Gate. Seven radical court nobles had walked out of Kyoto on foot. Not a blade had been drawn. Choshu had simply been told to leave — and it had left.

The expulsion radicalized the domain. The moderate Choshu leadership was gradually pushed aside by younger, angrier men who had seen the insult and wanted it answered. After months of organizing, the decision was made: Choshu would march on Kyoto, restore the expelled nobles, reclaim their position at court, and settle the account.

The force assembled was approximately 3,000 men — around 1,400 regular Choshu domain troops augmented by roughly 1,600 ronin 浪人 (rōnin) and radical sympathizers. Their commanders included Fukuhara Echigo, Kunishi Shinano, Masuda Uemonnosuke, Kijima Matabei, Kuzaka Genzui, and the court loyalist Maki Izumi.

The assault on August 20 concentrated at the Hamaguri Gate 蛤御門 (Hamaguri Gomon) — the Clam Gate — on the western face of the palace compound. Defending forces from Satsuma, Aizu, and Kuwana domains held the gate and the surrounding positions. The fighting was fierce. Choshu's men pushed hard at the gate — and the gate held.

The casualties tell the story in numbers: Choshu lost approximately 400 men. The defenders lost around 60. Kijima Matabei was killed in the fighting at the gate. Kuzaka Genzui committed seppuku 切腹 (seppuku) as the attack failed. Maki Izumi, the ideologue who had helped plan the assault, fell on his sword as the samurai retreated. The domain's senior retainers — Fukuhara, Kunishi, and Masuda — survived the battle only to be forced into seppuku afterward, executed to satisfy the shogunate's demand for accountability.

As Choshu's men retreated through the streets of Kyoto, fire broke out. The source and intent of the fires remain disputed by historians: some accounts hold that retreating Choshu troops deliberately set them as a final act of destruction; others suggest the fires started in the chaos of battle and the retreat and spread beyond any control. What is not disputed is the result. The fires burned for three days. When they were extinguished, approximately 28,000 structures — the densely packed wooden townhouses, temples, merchant quarters, and residential neighborhoods of the ancient capital — had been reduced to ash. The event was called Dondon-yake どんどん焼け (Dondon-yake), the Great Kyoto Fire of 1864. It was one of the worst urban disasters in Edo-period history.

The shogunate used the assault and the destruction as justification for the First Choshu Expedition — a massive punitive military force assembled to crush the domain permanently. Choshu, surrounded and outgunned, accepted humiliating terms and appeared broken.

It was not broken. A young samurai named Takasugi Shinsaku seized control of the domain's government, reorganized its forces into mixed-class militia units called Kiheitai 奇兵隊 (Kiheitai), and began rebuilding for the next war. By 1866, Choshu and Satsuma — the domain that had crushed them at the Hamaguri Gate — had formed the secret Satchō Alliance 薩長同盟 (Satchō Dōmei). By 1868, they had overthrown the Tokugawa shogunate together.

The men who set Kyoto on fire became the founders of modern Japan.