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.

At the end of the ninth century, Denmark comprised all areas bordering on the Kattegat, that is, the central part of southern Scandinavia. This chapter explores the origins of this conglomeration of territories and of its further history throughout the rest of the Viking Age and the early Scandinavian Middle Ages. Archaeology has become an increasingly important source for the study of the earliest political history of Denmark. New procedures have been developed, such as the excavation of large areas of settlement and improved dating techniques, notably dendrochronology. By and large there appears to have been a tendency towards political unification of Denmark throughout the Viking Age, but royal sovereignty over the entire medieval Denmark cannot be substantiated until the latest part of that period. The chapter also presents discussions on the North Sea empire, and the early medieval Danish kingdom, especially the political and social organisation of eleventh-century Denmark.

The killing of Knud Lavard in January 1131 started a period of dynastic strife in Denmark, which ended in 1157 when Valdemar I, became the ruler. His reign and that of his sons, Knud IV and Valdemar II constitute the period when a high medieval kingdom of European type emerged, consolidated by an ordered succession to the throne. The century following Valdemar II's death in 1241 saw political unrest which led to disintegration of the Danish kingdom in Scandinavia. The contrast between the Roskilde Chronicle and Saxo seems to reflect a serious political conflict in twelfth-century Denmark, between the old magnates' families who sought to protect their traditional rights and a new, more effective, and ruthless royal power of which St Knud was an early representative. The Danehof became the forum of negotiations between the king and a group of magnates who often opposed him. The chapter also talks about the Finderup murder of King Erik Klipping in 1286.

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.