It is said that this system was established in the process in which the ritsuryo-code-based nation was changed to a dynastic nation and the Imperial Court entrusted its administrative rights to the local administrative organs (kokuga [provincial government offices] and zuryo [the head of the provincial governors]).
律令国家が王朝国家へと変質し、朝廷から地方行政（国衙・受領）へ行政権を委任する過程で成立したとされる。