The primitive art of war was based on the leiđanger ("levy") organization in all of the Scandinavian countries, and thus the topography of the countries has great importance. Thick and large forests filled the inner part of Scandinavia as well as the Danish island realm, and made these countries difficult to traverse on land. Furthermore, for southern Denmark, the large woodlands in Holstein by Jutland's base formed a natural border toward Europe.

Since the settlements were along the coasts, communication seldom took place over land, but instead along the coasts and by the sea.

Given the topography of the countries, until the forests were cleared and routes by land made more passable, expeditions took place on sea, and attack from enemies also took place from the seaward side. The war organization that Norway, Sweden, and Denmark could procure was therefore attached to the sea and went out from near-shore settlements. The leiđanger system is known in Denmark from the provincial laws, which are preserved from around 1200, and reveal an organization that had its origins in the Viking Age. When exactly the leiđanger system arose is not known, but it seems to have been introduced almost simultaneously in all three countries. From around 1000, in the last part of the Viking Age, it is clear that the kings were able to raise themselves above the other Viking magnates with the help of the leiđanger organization.