Regardless of Kogoro and Shinsaku TAKASUGI, who took a cautious attitude towards the foreign powers (or who regarded the expulsion of the barbarians reckless), on June 27, 1863 the Choshu army under the command of Genzui KUSAKA attacked foreign vessels passing through the Kanmon-kaikyo Straight in Shimonoseki, starting a war against Western countries in accordance with the shogunal declaration of the expulsion of the barbarians at the behest of the imperial court.
5月12日、小五郎や高杉晋作たちのかねてからの慎重論（無謀論）にもかかわらず、朝廷からの攘夷要求を受けた江戸幕府による攘夷決行の宣言どおりに、久坂玄瑞率いる長州軍が下関で関門海峡を通過中の外国艦船に対し攘夷戦争を始める。