This chapter takes its cue from Chapter 1 in this volume, which presents a verticalization theory of language shift, and the case studies that test the theory within different American communities from the perspective of historical (socio)linguistics. First, the main tenets of the verticalization theory and its application to different communities in America, i.e. the five case studies, will be revisited. Second, the applicability of the theory to communities outside of North America will be further tested by comparing two Swiss migration case studies, one from North America and one from a region in today’s Ukraine. Finally, the merits of the verticalization theory will briefly be discussed within the context of historical sociolinguistics, where special attention will be paid to the challenges of reconstructing the social histories of linguistic communities in diasporas in the past, and of interpreting surviving linguistic data illustrating maintenance and shift.