Conventional geography's boundary line between a "Southeast Asia" and an "East Asia," following a "civilizational" divide between a "Confucian" sphere and a "Viet­nam aside, everything but Confucian" zone, obscures the essential unity of the two regions. This article argues the coherence of a macroregion "Sino-Pacifica" encom­passing both and explores this new framework's implications: the Yangzi River basin, rather than the Yellow River basin, pioneered the developments that led to the rise of Chinese civilization, and the eventual prominence of the Yellow River basin came not from centrality but rather from its liminality—its position as the contact zone between Inner Eurasia and Southeast Asia.