Dialect levelling

Dialect levelling (or leveling in American English) is an overall reduction in the variation or diversity of features between two or more dialects. Typically, this comes about through assimilation, mixture, and merging of certain dialects, often by language codification, which can be a precursor to standardization. One possible result is a koine language, in which various specific dialects mix together and simplify, settling into a new and more widespread form of the language.

Dialect levelling has been observed in most languages with large numbers of speakers after industrialization and modernization of the areas in which they are spoken. However, while less common, it could be observed in pre-industrial times too, especially in colonial dialects like American and Australian English or when sustained linguistic contact between different dialects over a large geographical area continues for long enough as in the Hellenistic world that produced Koine Greek as a result of dialect leveling from Ancient Greek dialects.