linguistic:paraphrasing, information:extraction
The Middle Ages

During a period of Christianization and state formation in the 10th–13th centuries, numerous Germanic petty kingdoms and chiefdoms were unified into three kingdoms:

According to historian Sverre Bagge, the divisions into three Scandinavian kingdoms (Denmark, Sweden, Norway) makes sense geographically, as forests, mountains, and uninhabited land divided them from one another. Control of Norway was enabled through seapower, whereas control of the great lakes in Sweden enabled control of the kingdom, and control of Jutland was sufficient to control Denmark. The most contested area was the coastline from Oslo to Öresund, where the three kingdoms met.

The three Scandinavian kingdoms joined in 1397 in the Kalmar Union under Queen Margaret I of Denmark. Sweden left the union in 1523 under King Gustav I of Sweden. In the aftermath of Sweden's secession from the Kalmar Union, civil war broke out in Denmark and Norway—the Protestant Reformation followed. When things had settled, the Norwegian privy council was abolished—it assembled for the last time in 1537. A personal union, entered into by the kingdoms of Denmark and Norway in 1536, lasted until 1814. Three sovereign successor states have subsequently emerged from this unequal union: Denmark, Norway and Iceland.

The borders between Denmark, Norway and Sweden acquired their present shape in the middle of the 17th century: In the 1645 Treaty of Brömsebro, Denmark–Norway ceded the Norwegian provinces of Jämtland, Härjedalen and Idre and Särna, as well as the Baltic Sea islands of Gotland and Ösel (in Estonia) to Sweden. The Treaty of Roskilde, signed in 1658, forced Denmark–Norway to cede the Danish provinces Scania, Blekinge, Halland, Bornholm and the Norwegian provinces of Båhuslen and Trøndelag to Sweden. The 1660 Treaty of Copenhagen forced Sweden to return Bornholm and Trøndelag to Denmark–Norway, and to give up its recent claims to the island Funen.

In the east, Finland was a fully incorporated part of Sweden from medieval times until the Napoleonic wars, when it was ceded to Russia. Despite many wars over the years since the formation of the three kingdoms, Scandinavia has been politically and culturally close.