In 1545, he entered into an alliance with Norimasa UESUGI, Haruuji ASHIKAGA (one of the Kogakubo, who were descendants of one of the Ashikaga families and held the office of the regional administrator in Kanto), and others to assemble a vast allied force consisting of some 80 thousand soldiers, and proceeded to attack Kawagoe-jo Castle in concert with Yoshimoto IMAGAWA, the ruler of Suruga Province.
天文14年（1545年）には駿河国の今川義元と連携し、上杉憲政や古河公方の足利晴氏らと連合した8万の大軍で河越城を攻める。