Well thats how most kingdoms in that age got founded. Even british kingdoms. There is a saga behind why he became king of such a big kingdom. He wanted to marry the local gal, but she said "If you make your kingdom as great as the Danes and Sweds, I will marry you!" And he did. Negotiated union with other Jarldoms and fhought those that did not comply. And through that time, he has not cut his hair an inch. Wich granted him the title, Hårfagre (or Fairhair for ye english speakers). And yes, he got the gal. I belive you are thinking of Haakon the Holy who killed anyone who did not convert to christianity. Even christians can be barbarians.