Japan, included in this group of small empires, had a system of ritsuryo kokka, where the emperor was in a position comparable to the emperor of China and Japan had an imperial structure in which Japan was regarded as the center of the world, similarly to Tang.
その中にあって日本の律令国家体制では、天皇は中国の皇帝と並ぶものであり、唐と同様、日本を中華とする帝国構造を有していた。