Internal consolidation in the high medieval Scandinavian kingdoms meant that more energy and resources could be directed to foreign affairs, which led to expansion in directions that were determined by the geographical positions of the three kingdoms and other factors. Norway expanded towards the islands of the western sea, Sweden towards Finland and the eastern Baltic. The Danish kingdom found the chief outlets for its foreign energies in north Germany and along the Slavonic south coast of the Baltic. After 1300 inter-Nordic relations were, to a much higher degree than before, determined by internal political conditions in Sweden. In 1319, the first of the medieval Scandinavian unions was established. It was clearly an outcome of the inter-Nordic entanglement which had started in the mid-thirteenth century, not least on the initiative of the consolidated Norwegian monarchy under Håkon Håkonsson. The process had now gone too far to be stopped by the new-found cautiousness of Håkon V in his last years.

The main tendencies in the development of Scandinavian political organisation in the high Middle Ages were centralisation and growth of public authority under the monarchy, the Church, and the secular aristocracy. This chapter outlines the development of three Nordic kingdoms that grew into more state-like entities, until 1319 when the first of the Nordic unions was established between Norway and Sweden. Danish struggles over the succession to the throne from the 1130s to the 1150s were followed by the strong and expansionist Valdemarian monarchy which once more made Denmark the leading kingdom in Scandinavia. In Norway, the Norwegian church was centralised under the archbishop of Trondheim in 1152-3, and in the following decades the first steps were taken towards a nationally organised system of government. Scandinavian kingship entered a new phase in the high Middle Ages, reflected by the introduction of royal unction and coronation. There may have been early royal initiatives in provincial thing legislation in the Scandinavian kingdoms.

By the Scandinavian kingdoms are understood the kingdoms of Denmark, Norway and Sweden. The three Scandinavian kingdoms were established long before 1200, as were also, with some exceptions, the borders that were to remain until the great changes of the seventeenth century. The old military system in the Scandinavian countries was the popular levy, Norse leidang, Danish leding, Swedish ledung, primarily intended for sea warfare. Its origin can probably be traced back to the Viking age in Denmark and Norway. Earlier generations of scholars often described social change in the Scandinavian countries during our period as a transition from a 'society of kindred' to a 'society of the state'. The formation of an elite can be traced in the cultural field as well as in the social, economic and political ones. The growth of public justice is contributed to divisions and competition within the elite.