To secure their realm, the Swedish kings, notably Gustav Vasa (r.  1523–1560) and Eric XIV (r.  1560–1568), encouraged farmers to settle these vast wilderness regions, which in turn were used to the traditionally slash-and-burn agriculture.

These settlements faced several problems, from conflicts with the original populations of Sami people and Karelians to harsh conditions living in frontier lands during war times.

The fact that slash-and-burn itself requires a relatively low human population density or a continuing supply of new "frontier" lands, also caused overpopulation and by the late 16th century forced migration by Forest Finns from Savonia (Swedish: Savolax) and Northern Häme (Tavastland).

Another migration route started from Medelpad and continued through the early 17th century on crown lands in the provinces of Dalarna, Värmland and Dalsland, among others, to occupy the areas immediately adjacent to the border with Denmark–Norway.

The largest concentration of settlements, however, was in the forest-rich eastern part of Hedmark, close to the border of Sweden, in what today is denoted as Finnskogen in Norwegian and Finnskog[arna] in Swedish (literally "Finn Forest[s]").

In April 1823, six Swedish and six Norwegian Forest Finns traveled to the capital Stockholm in what was called "Tolvmannamarsjen" (English: The march of the twelve men).

They brought a petition with 600 signatures demanding their own common church congregation (Kirkesogn) with a Finnish speaking priest right on the Norway-Sweden border.

[3] In Sweden, the migration of the Forest Finns was not only well accepted at first, but also masterminded and encouraged by the kings, notably Charles IX (r.  1604–11) and Gustavus Adolphus (r.  1611–32).

Among attractions offered for the migrating Finnish farmers in Sweden were seven years total exemption of all taxation and the prospect of ownership of large fertile plots of land.

The Forest Finns with their demanding slash-and-burn agriculture were suddenly considered an economic threat by increasing the cost of charcoal by burning off now valuable timber.

During the previous two centuries, various laws and regulations had been passed to speed up the "Swedification" process to the Forest Finns, including total banning of the use of Finnish language.

During the reign of Christina, Queen of Sweden, a proclamation by the Fryksdal Hundred assembly in 1646 called for the killing and the burning of houses of all those Finns who did not want to learn Swedish.

The Dano-Norwegian authorities in Copenhagen were allegedly in favor of the de facto immigration and their slash-and-burn agriculture due to the relatively high yields of rye production, compared to traditional Norwegian staples.

The 1686 census still exists and provides valuable information about the extent of the immigration to Norway at that time, and a total of 1,225 people (including 160 of mixed Finnish-Norwegian descent) were accounted for.

Societal advances, including a changing emphasis on pasture-based agricultural models, improvements in education and communications, altered the foundations on which the Forest Finn’s lifestyle depended.

Long-term pressure to adapt, and the influence of intermixing with the extant Scandinavian populations in concert with economic and societal change led to the eventual loss of their identity as Forest Finns.

He collected folklore and other ethnographic data as well as genealogical information, the latter partly because he wanted to improve the social circumstances of the Forest Finns and to prevent Sweden from taking ownership of their land.