Kanto Gobunkoku (関東御分国)
Kanto Gobunkoku was the group of provinces ruled and administered by Shogun families (Kamakuradono) during the Kamakura period. Kanto Gobunkoku also included the provinces ruled by the Kamakura regional government, installed by the Muromachi bakufu (Japanese feudal government headed by a shogun) in the Muromachi period. It was also called Kanto Chigyokoku or Kanto Bunkoku.
Incidentally, the word "Kanto" in this case indicates the Kamakura bakufu itself rather than the location of the provinces, (today, "Kanto" specifies the central-eastern region of Japan including Tokyo, and Kamakura, where the bakufu was also established) therefore Kanto Gobunkoku meant not just the provinces located in the eastern region, but also the provinces located in the western part of Japan under the ruling of the Kamakura bakufu.
Kanto Gobunkoku during the Kamakura period
The form of Kanto Gobunkoku in the Kamakura period was that the family/clan members or the retainers of the Kamakura bakufu were recommended to the Imperial Court for nomination as provincial officials, in order to rule the provinces as the officials of Kokugaryo (Imperial province) and properly earn revenue from the province.
In 1185, the number of Kanto Gobunkoku reached the highest at 9, although the number of Kanto Gobunkoku decreased to 4 during the reign of MINAMOTO no Sanetomo, the third and last shogun of the Kamakura bakufu. While Kanto Gobunkoku played a great role in securing the rule of the Kamakura bakufu during it's time, it's importance was reduced once the shogunate order was established and stabilized, and the number of provinces gradually decreased. The Kanto Gobunkoku that remained until the fall of the Kamakura bakufu were Suruga Province, Sagami Province, Musashi Province and Echigo Province, while the officials assigned to Sagami Province and Musashi Province were regents/cosignatories of the Kamakura bakufu.