The primary purpose of this research is to analyze the formation of international custom of medieval East Asia under the system of the Great Ming Code. It focuses on Korea’s policies regarding Japanese crimes in the fifteenth century. This study particularly investigates how the Great Ming Code affected the East Asian system of order. We find that Confucianism, which was the basis for the Great Ming Code, had a great influence on the formation of customs in East Asia in such areas as the establishment of patriarchal authority, filial piety, and the five punishments system. This study also investigates how etiquette, which served as a foundation for diplomatic regulations, affected Korea-Japan relations during the fifteenth century. It also analyzes Joseon (Korea)’s control policies against illegal acts committed by the Japanese, who tried to enter Joseon for economic gain, from the perspective of the Great Ming Code.

Custom is a source of Islamic law in general and Siyar (Islamic international law) in particular. Islamic jurists have set out the elements and conditions of customs for general jurisprudential purpose. However, no one has, to the authors’knowledge, formulated them from Siyar perspective. This paper is an attempt to fill this gap by tracing two important elements of an international custom, namely frequent and dominant general practice of States, and acceptance of that practice as law. These two will constitute a valid custom provided they fulfill certain conditions, most importantly that the custom must not conflict with Shari’ah or the spirit of Shari’ ah.