Hm, I dunno... things are moving pretty slowly ever since the prologue ended. I don't really see an invasion happening, and Thorfinn seems fine with how he gets treated. Einar will probably be the catalyst for something to happen eventually since so much time was spent on him already.

I think if the author is going to continue his theme of discovering how to be a "true warrior" he will eventually shift Thorfinn's reason for fighting from aggression or revenge to protecting others.