In each of the Scandinavian kingdoms, unification goes hand in hand with conversion. By officially accepting and imposing Christianity, kings achieved two goals. First, they removed the ability of their competitors to use religion to build networks of friendship and spiritual relationships. The competitors were unable to use paganism for that purpose, since public pagan rites were outlawed, as well as Christianity, since the kings controlled the bishops and thus access to the rituals of that religion. Second, they acquired all the advantages of Christianity, including its legitimizing power, the administrative know-how of its clergy, and its prestigious international connections.
In the competition for power among chieftains, some came out on top, with the result that the first millennium saw fewer and fewer serious contenders as the centuries passed, until only three remained in the early second millennium. They were the kings of Denmark, Norway, and Sweden, and, not coincidentally, all of them were Christians. They needed Christianity and the church, for they had become so powerful that they were unable to create personal relationships with their followers and subjects because there were too many of them. At that point, Scandinavian kings institutionalized their power. They used the church to help create and legitimize structured kingdoms that were held together by more than gift exchange relationships. The church provided an ideology of kingship that emphasized, among other things, that there could be only one king, just as there was only one God and only one church.