It is said that the reason why the families of Chiba no suke and Kazusa no suke joined Yoritomo was not because they were followers of the generations of the Genji family as stated in "Azuma Kagami" (The Mirror of the East); rather, they supported Yoritomo to fight back against the attacks by the Fujiwara clan of Shimosa, who was aligned with the Taira family, and the Satake clan of Hitachi in an attempt to recover their lost territories, which was a revival gamble.
千葉介、上総介一族が、頼朝に加担したのは、『吾妻鏡』にいうような、両氏が累代の源氏の郎等であったからではなく、平家と結んだ下総の藤原氏、そして常陸の佐竹氏の侵攻に対して、頼朝を担ぐことによってそれを押し返し、奪い取られた自領を復活する為の起死回生の掛けであったといわれる。