First, it is necessary to define the spatial scope discussed in this book. The term “East Asia” used in the title is, in fact, a shorthand for the East Asian Mainland. As a geographical concept, East Asia undoubtedly refers to the eastern part of Asia, though the specific regions it encompasses are not entirely clear. Broadly defined, East Asia includes both Northeast and Southeast Asia. In this book, however, the East Asian Mainland does not include the predominantly peninsular and insular regions of Southeast Asia. In terms of current national administrative divisions, North Korea, South Korea, and Japan, countries that are narrowly defined as East Asia or Northeast Asia, are peninsulas and islands.