The establishment of unique and particular relationships is the precondition for identifying a specific space among areas. Such relation network, different from that of other regions, exercises greater influence on all members involved, in either direct or indirect fashion. From this perspective, it is not a group of individual nations and people geographically located in the same place that builds a region. The presence of its own social system and relations is required for emergence of regional identity. East Asia also had its own relation structure in the light of this fact. The region has experienced changes in internal structure or relationships over time, which could serve as the criterion for dividing periods of East Asian history. This paper studies such changes, focusing on diverse factors such as the investiture system, treaty relation, development of offshore Asia, formation of the Mongol Empire, the tribute trade system, and mutual trade (hushi) system. As countries were incorporated in a certain regional order, they adopted a specific pattern of behavior according to the order and thus enabled to carry out exchange without a fear of armed conflict. With the Western-dominated international order established in the end of 19th century, however East Asia was no longer able to maintain its independent network of relations.