The Battle of Shimosuwa was a battle of the Boshin War which was fought in late December 1867 between the pro-Imperial army of the Choshu Domain and the pro-Shogunate army of the Nagaoka Domain in present-day Nagano Prefecture. Mori Takachika's Choshu army invaded Shinano Province in November 1867 and captured Iida, the capital of South Shinano, prompting the Nagaoka general Yanagisawa Sadamori to march south in a bid to reclaim South Shinano from the Emperor's army. Takachika decided to march out to intercept this army, meeting it at Shimosuwa. The Choshu left flank outflanked the Nagaoka army, which was massacred from two sides. Sadamori was killed and his army scattered, and the Choshu army proceeded to take the provincial capital of Matsumoto with no losses. At the start of 1868, Takachika also massacred the remnants of the Nagaoka army, paving the way for an advance on Kofu in Kai Province.