The shogunate side (the Aizu clan and Shinsengumi) forcefully made a second conquest of Choshu on the pretext of its nominal submission to the shogunate accompanied by secret armament as well as Omura's secret trading with foreign countries.
長州藩の武備恭順や大村益次郎たちによる秘密貿易を口実として幕府側（会津藩・新撰組）は、第二次長州征討（長州征討）を強行してくる。