However, after World War II, Tadashi I SHIMODA wrote "Chuseiteki Sekai no Keisei" (The formation of the medieval world) and presented the idea of 'Zaichi ryoshu sei' (the local lord system) that relates the process of the dismantling the ancient nation with the institution of slavery sustained by the nobility and the temples and shrines, with the formation of the medieval nation with a feudal system supported by the samurai class.
しかし、戦後になって石母田正が『中世的世界の形成』を著し、武士が在地領主として在地を支配していく過程と貴族・寺社による古代奴隷制国家の解体と武士による中世封建制国家の形成を関連付ける「在地領主制」の考え方を打ち出した。