Histories of East Asia traditionally emphasize China and Japan, and neglect Korea and Vietnam. Essentially, 20th century East Asia is re-written into the past, as though China and Japan was always the core of East Asian development. This is not at all how East Asia developed. Chinese prehistoric cultures became historic in the 18th century B.C. Japan was not part of East Asia for over 2300 more years. By studying periods of Chinese unity and disunity, and their effects on China's neighbors, Korea and Vietnam, a distinct culture zone, East Asia, gradually emerged, and slowly included Japan....