Changes in social structure often lead to mobility and migration. Urbanisation is one important outcome of mobility and migration. Mobility, migration and urbanisation lead to dialect contact, that is, between speakers of mutually intelligible varieties. This chapter first introduces general concepts such as diffusion and supralocalisation, and then moves on to discuss sociolinguistic models developed for the analysis of dialect contact, including the theories of koineisation and new-dialect formation, based on principles such as accommodation and salience. Case studies are taken from medieval Spain, Early Modern New Mexico and twentieth-century Norway. The chapter also addresses the role of new speakers in contact situations, based on an example from sixteenth-century Tuscany, and ends with a short discussion of sociolinguistic typology.

In recent decades, scholars have examined the genesis of Jewish language varieties, particularly Yiddish, as well as Modern Hebrew, drawing intriguing parallels with creole formation processes. This chapter delves into the ecological aspects of language contact, comparing the sociohistorical and linguistic contexts of Jewish language emergence with Caribbean plantation creoles. Particular emphasis is placed on Judeo-Spanish (Ladino), tracing its linguistic trajectory following the traumatic expulsion of Sephardic Jews from Spain in 1492. By applying the “Founder Principle,” the research investigates the linguistic repertoires of founding populations, examining their social stratification, literacy capabilities, familial structures, and intricate social networks.

From a uniformitarian perspective, I interpret the emergence of Old English as the outcome of colonization and language contact. Likewise, I argue that its spread and speciation into so many varieties around the world, including creoles and pidgins, are consequences of different instances of colonization, which varied according to whether this involved settlement, exploitation, or trade. Each colonization style produced a different population structure, which in turn influenced how the language was appropriated and restructured by its non-heritage speakers. In England itself, one must invoke how the colonization of the land by other European nations subjected the language to the superstrate influence of the colonizers, who shifted to it. Ecological factors such as population structure (which determine patterns of social interactions and language transmission) and periodization (associated with particular moments of language shift or appropriation) help account for the differential evolution of English around the world.