The duty of Kanto Kanrei was originally to assist the Kogakubo (Kamakura kubo (Governor-general of the Kanto region)), and since Kagetora succeeded in regaining control of Kogagosho which was invaded by the Hojo clan and put forward Fujiuji ASHIKAGA, original legitimate successor, as Kogakubo, it was also recognized by the Imperial court, bakufu and territorial lords in the Kanto region that Kagetora inherited the family headship of Uesugi clan and assumed Kanto Kanrei.
関東管領の職は本来、古河公方（鎌倉公方）を助けることが職務であるため、北条に侵略されていた古河御所の奪還と、本来の正統な相続者である足利藤氏を古河公方に擁立することに成功した景虎は朝廷および幕府からも関東の諸大名からも認められた上杉氏の家督相続と関東管領就任であった。