After Emperor Kōmei issued the Order to expel barbarians, tensions in Japan between Shogunate and Imperial forces began to boil over into all out conflict. Amongst the first to make a move was the Aizu clan, who, under the young Daimyo Matsudaira Katamori, sought to expand their domain. War was declared against the Imperial Utsunomiya clan in the winter of 1864.
The first battle was fought at Yaita, where the Aizu general Yamakawa Hiroshi bested an Utsunomiya army sent out to defeat him. That spring he moved on the Utsunomiya stronghold of Tochigo, eventually taking it in a bloody siege. This marked the end of Utsunomiya power in the region and also drew the support of the Shogun for the Aizu clan.