The process can vary from outright suppression of an indigenous language to adoption of a language seen as more useful (e.g. more widely spoken) or conferring higher status. Trade, urbanisation, public education and mass media each accelerated the process and offered dominant groups new means to drive the process still further.

Tell-tale signs of forced assimilation might include withholding education in an indigenous language or denying access to public services or employment for its speakers (unless there really weren't the numbers for it to be a viable proposition), or suppressing or penalising its publication or broadcast. Promotion of a non-indigenous religious model or perception of the past are also used to erode traditional allegiances and identity.

Another top-down approach is of course literal colonisation, settlement of speakers of the privileged language, often with economic advantages (e.g. land grants, government jobs or contracts), forcing native speakers to adopt the dominant tongue for work or sometimes even making them a minority.

It isn't always coercive or associated with migration, and sometimes the "metropolitan" language is itself partly assimilated into a pidgin or creole tongue including indigenous elements: the most widespread lingua franca drawing on different elements is probably Swahili, grammatically Bantu but with large borrowings from Arabic and spoken far beyond the former area of Arab dominance: in Europe, Celtic cultural expressions are similarly thought to have spread ahead of any movement of people or change of ruling elite.