A persistent problem in Sino-Tibetan linguistics is that Chinese is characterized by a mix of lexical, phonological, and syntactic features, some of which link it to the Tibeto-Burman languages, others to the Tai-Kadai, Hmong-Mien, and Mon-Khmer families of Southeast Asia. It has always been recognized that this must reflect intense language contact. This paper develops a hypothesis about the nature of that contact. The language of Shang was a highly-creolized lingua franca based on languages of the Southeast Asian type. Sinitic is a result of the imposition of the Sino-Tibetan language of the Zhou on a population speaking this lingua franca, resulting in a language with substantially Sino-Tibetan lexicon and relict morphology, but Southeast Asian basic syntax.