1219 January, with the death of his cousin, the third shogun MINAMOTO no Sanetomo, the position of Seitaishogun (commander-in-chief of the expeditionary force against the barbarians) becomes empty, and a month later, he raises an army in hope for this position.
建保7年（1219年）1月、従兄弟の三代将軍源実朝の死により征夷大将軍の座が空席となると、翌月その位を望み挙兵する。