With the establishment of the Kamakura bakufu (Japanese feudal government headed by a shogun), samurais, especially in the Kanto region, became Gokenin (lower-ranking vassals in the Kamakura and Edo periods) who entered into the service of the Kamakura bakufu.
鎌倉幕府の成立に従い、主に東国の武士は鎌倉幕府に奉公する、御家人となった。