> I don't know why it is like that, but perhaps a reason is that Viking culture was very revenge and honor based. But this mentality was destroying society so authorities worked hard for hundreds of years to change this mentality.

Or maybe it really sprung out of the Christian influence that came after the Viking culture, with teachings like: "Love your enemies" [Matthew 5:44 - https://www.biblegateway.com/passage/?search=Matthew+5%3A44&...]?