On the other hand, in his position as the Emperor, Gotoba had expanded armaments to purge the pro-shogunate forces from his rule, and thereafter he took up arms, in 1221, against Yoshitoki, who was considered an enemy of the Emperor, in order to overthrow the shogunate.
一方で後鳥羽天皇は軍備を拡張し、院政内の親鎌倉派を粛清した後、承久3年（1221年）、義時を朝敵として倒幕の兵を挙げた。