East Yi West Xia (Chinese: 夷夏東西說; pinyin: Yí Xìa Dōngxī Shuō) is an obsolete theory which proposes that the culture of the Chinese Shang dynasty was established by two ethnic groups; namely, that the Western part of the Shang dynasty was developed by the Xia ethnic group, and the eastern part of Shang dynasty was developed by the Yi ethnic group.
In 1983, the ruin of Yanshi Shang City was discovered and identified as the Erligang culture.
Though largely replaced and modified by later further research, Fu Sinian's theory entered the history as a landmark in Chinese historiography.
It essentially questioned ethnic homogeneity sometimes postulated as the route of Chinese civilization.
See for an English language summary of this theory: Chang Kwang-chih, 'China on the Eve of the Historical Period' in: Loewe, Michael and Edward L. Shaughnessy (eds.