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The Siege of Otsu occurred in early September 1867 when the pro-Imperial Choshu Domain besieged the town of Otsu in Omi Province, first taking it from the pro-Shogunate Nagaoka Domain and restoring the independence of the Hikone Domain, and then taking it from the nascent Hikone Domain after the Hikone Domain continued to side with the Tokugawa Shogunate in the Boshin War.

Background[]

Following the Battle of Lake Biwa in July 1867, Choshu Domain daimyo Mori Takachika attempted to finish off the pro-Shogunate Nagaoka Domain's field armies in the Kansai region by pursuing and destroying Ikeda Nagateru's large army. Nagateru was wounded in an assassination attempt by the Choshu shinobi Sukeomi, but his army survived and outmaneuvered Takachika's general Takasugi Shinsaku; the Nagaoka army was also able to capture Otsu in Omi Province from the Tottori Domain before marching further north. Shinsaku and his army marched on Otsu, intent on recapturing the town and pursuing the Nagaoka army.

Siege[]

Shinsaku's 2,736-strong Choshu army found Otsu defended by a garrison of 300 troops under Matsuoka Tadamori. The Choshu army took Otsu without any casualties, while the garrison was overwhelmed by Choshu's superior numbers. Shinsaku, hoping to avoid having to enforce public order in the province, liberated the Hikone Domain, establishing Ii Sanekuni as the ruler of the province. However, Ii turned out to be a supporter of the Shogunate as well, and, recalling past events, Shinsaku predicted that it would only be a matter of time before Choshu's allies declared war on the pro-Shogunate clan and forced Choshu to betray Hikone. Rather than waste time and allow the Hikone clan to consolidate its strength, Shinsaku preemptively betrayed the Hikone Domain within days of establishing its independence and led a second assault on the city. The Choshu army took the city with just 2 losses, but its betrayal of Hikone cost Takachika much of the credibility he held with his allies. Omi was placed under Choshu occupation, and Choshu was once again forced to turn its attention to the east after the Kanazawa Domain captured Mino Province and crushed the Gujohachiman Domain.

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