Crusader Kings II

[Myth]

What? Wessex can be stomped early on if one of the two Danish dukes goes on a prepared invasion AND Jorvik joins as well. Otherwise you will win a war of attrition. Once one of the Karlings secures dominance in Catholic europe and Holy Wars start flying their way, the Norse run out of steam pretty quick. Also, with the nerfing of the pagan Subjugation CB to once per life, and the AI's inability to play well under Gavelkind succession, you only have to survive the initial onslaught IMO.