I think it had something to do with Len Wiseman waiting too long to find the right actress. But either way, there was a huge difference between the memory and Rise of the Lycans. For example, in Lucian's Blood Memory, Sonja (why does it seem like almost everyone calls her Sonya?) was basically a damsel in distress. If you've seen Rise of the Lycans then you know that this is DEFINITELY not the case. Also, the first thing you notice about her is how her hair was changed from blonde to black. This was done for one obvious reason: so Sonja would look just like Selene.
I don't think you can really say who started it now that I think about it... you can, however, say that the first battle that started an all-out war was when Raze led the Lycans against Castle Corvinus (to save Lucian and probably to get revenge).