Following Finland's incorporation into Sweden in the 12th century, Swedish became the dominant language in administration and education, although Finnish recovered its predominance after a 19th-century resurgence of Fennomanic Finnish nationalism (also working to assure Russia of the Grand Duchy's loyalty).
The Finnish national awakening in the mid-19th century was the result of members of the Swedish-speaking upper classes deliberately choosing to promote Finnish culture and language. And they didn't just promote the language. They finnicized their family names, learned the language, and made a point of using it both in the society and at home, giving their children what they missed themselves: the Finnish mother tongue. However, another faction of the Swedish-speaking elite did not wish to abandon Swedish, as they felt it was a guarantee that Finland would remain within the cultural sphere of Western Europe.
In 1892 Finnish became an official language and gained a status comparable to that of Swedish, and within a generation Finnish clearly dominated in government and society. Inevitably, this situation made for conflict between the supporters of the two languages. In the beginning, the conflict only involved the upper social strata, but the population at large was drawn into it after universal suffrage was implemented in 1906.
The last surge of Finnization frenzy came in the 1920s. After Finland's independence followed strained relations with Sweden in connection with the Finnish Civil War and the Åland crisis, and the attitudes to the language issue sharpened to become a prominent feature of domestic politics during the 1920s and 1930s. This time the surname Finnization was chiefly a middle class phenomenon.
In independent Finland's constitution, the minority language (Swedish) was given far-reaching privileges. The language strife was thereafter centered on these privileges and the role of Swedish in universities, particularly regarding the number of professors lecturing and examining in Swedish. Then, at the resettlement of over 400,000 Karelians after the Winter War, the Swedish-speaking minority feared that new Finnish-speaking settlers would change the linguistic balance of their neighbourhoods. These issues were ultimately settled by the fennoman Prime Minister and later President of Finland Juho Kusti Paasikivi in a way too generous to attract much criticism from the Finland-Swedes.