You are right in assuming that there is a lot of complex factors that is important here, in addition to truly answer your question you also need to go through the whole history of the Nordic countries, from the beginning of the Viking Age to modern day, something I sadly don’t have the knowledge to do. Therefore, I will be focusing on the Viking age and medieval age in Scandinavia and more specifically Norway to try to answer why society changed from the system where the families where responsible for revenging crimes done too their kin to a system where the king appointed people to make sure the laws are followed and punish those who broke them.

Firstly, I want to say that the Vikings had a great sense of justice. They had laws forbidding both murder and rape, and punishments for committing these acts. The Things where a well-developed system, and relatively democratic for its time too. On the Things, the people of an area agreed to laws, judged in disputes and decided on common policy. For example, when the Norwegian kings wanted to convert the Norwegian population to Christianity they went to the Things to debate with the farmers. The problem with the thing system, from our perspective, is that it had no police force. There were no one with the specific job of making sure the decisions of the Thing were held, and that the criminals were made to pay the fine they got. It was the family of the offended who were responsible for this and if the family of the criminal did not want to pay the fine he was obliged to pay according to the Thing it was the duty of the family of the offended to take revenge and restore their honor. This could be done through revenge, i.e. killing some part of the criminal’s family, or through a duel often called holgang. The concept of maintaining your honor was so important that in one set of regional laws, failing to revenge an insult would mean that you would lose your rights and reputation.

So that was a basic introduction to the Nordic legal system in the Viking age, so how did this change over time? Well the changes came with the kings and their attempt to build up their power in the countries they ruled. In the beginning, they supported the system of the things, because the system allowed the kings to govern the famers in a reasonable way and therefore the Thing system was strong at the end of the Viking age. In the late Viking age or early medieval age the role of the kings changed, they were no longer supposed to be warriors, but rather administrators and judges. To help them do this they had many people in the hird, and these people was at the various Things making sure that the kings law was being followed. In Norway the first of these king was Olav Kyrre(the peacefull). With the role of the Kings and the local lords changing so did the power of the judicial system. There where now people to make sure that the laws where being followed, as well as people to punish the criminals the amount of people killing for honor was reduced. An important factor in this change was the fact that the Scandinavian countries where being converted to Christianity and with it came a lot of external customs, like laws, and a new way of living, in which the old ideals of honor and revenge had no place anymore.

In Norway, the final move away from the system described in the beginning came in 1274 when one national law affecting all parts of Norway was made. This law was made by the king and accepted by the thing, rather than being made by the things, thus the king was a lot more involved in it, and breaking it would mean you were in a conflict with the king, and therefore had to pay him a fine for breaking his laws.