In the eleventh century the northern and central parts of the Scandinavian peninsula were occupied by a people who are often called Lapps but who called themselves Saami. Contemporaries distinguished four main groups of Scandinavians: Danes, Götar, Svear and Norwegians or Northmen. By the year 1200 most of the territory occupied by these Scandinavians had been incorporated in the three medieval kingdoms: Norwegian kingdom, Danish kingdom, and Swedish kingdom. The Danish kingdom was the first to be firmly established. The Swedish kingdom was formed by the unification of the Götar and the Svear. The earliest Scandinavian historians, writing in the twelfth and thirteenth centuries, believed that the Danish kingdom had existed since time immemorial and that the kingdoms of Norway and Sweden were relatively recent creations formed by the unification of many small kingdoms. The founder of the medieval Norwegian dynasty was Harald Hardrada. The earliest of the provincial laws, for the west Norwegian province, survives in a twelfth-century version.

The death of King Sigurd Crusader in 1130 marked the transition from a century of relatively peaceful internal conditions in Norway to a century of frequent struggles over the succession to the throne which are referred to as the Civil Wars. Due to and during these struggles, the development of a more centralised and better organised Norwegian kingdom gained momentum. This resulted in a period of internal consolidation between the last outbreak of hostilities in 1239-40 and the death of King Håkon V Magnusson in 1319. For the consolidated monarchy the right of inheritance played a central role. The period of early 1260s to about 1400 has been termed the Norwegian age in Icelandic historical research. King Magnus Law-mender laid down the principle that there should be one king over the whole Norwegian dominion, both inland and over the tributary lands. This meant that Iceland was considered part of the Norwegian realm both constitutionally and administratively.

The Viking Age and early Middle Ages saw the beginning of political unification in the larger territories, leading to the creation of the kingdoms of Denmark, Norway and Sweden, and the Free State of Iceland. The early political unification was the outcome of political decisions made by individuals, and of military force. The formation of the kingdoms involved the development of a more elaborate and formalised military organisation. The breaking up of the Danish North Sea empire and the consequent weakening of the Danish kingdom made it possible for Norwegian kings to establish a more permanent rule over most of their later territory. In Sweden the tendencies towards political unification came later and were weaker than in Denmark and Norway. In the process of political and social transformation Christianity and the Church were of crucial importance. Christianity and its ecclesiastical organisation were also means of enhancing the kings's power and prestige.