Mainland Southeast Asia linguistic area

The Mainland Southeast Asia (MSEA) linguistic area is a linguistic area that stretches from Thailand to China and is home to speakers of languages of the Sino-Tibetan, Hmong–Mien (or Miao–Yao), Tai–Kadai, Austronesian (represented by Chamic) and Austroasiatic families. Neighbouring languages across these families, though presumed unrelated, often have similar typological features, which are believed to have spread by diffusion.James Matisoff referred to this area as the Sinosphere, contrasted with the "Indosphere", but viewed it as a zone of mutual influence in the ancient period.

The Austroasiatic languages include Vietnamese and Khmer, as well as many other languages spoken in scattered pockets as far afield as Malaya and eastern India. Most linguists believe that Austroasiatic languages once ranged continuously across southeast Asia and that their scattered distribution today is the result of the subsequent migration of speakers of other language groups from southern China.

Chinese civilization and the Chinese language spread from their home in the North China Plain into the Yangtze valley and then into southern China during the first millennium BC and first millennium AD. Indigenous groups in these areas either became Chinese, retreated to the hill country, or migrated to the south. Thus the Tai–Kadai languages, today including Thai, Lao and Shan, were originally spoken in what is now southern China, where the greatest diversity within the family is still found, and possibly as far north as the Yangtze valley. With the exception of Zhuang, most of the Tai–Kadai languages still remaining in China are spoken in isolated upland areas. Similarly the Hmong–Mien languages may originally have been spoken in the middle Yangtze. Today they are scattered across isolated hill regions of southern China. Many of them migrated to southeast Asia in the 18th and 19th centuries, after the suppression of a series of revolts in Guizhou.

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