If you really want to be accurate about history in what is now Sweden, let’s also mention the horrific mass graves discovered in Birka and surroundings which seems to imply that massacring whole villages, women and children included , was commonplace even before Viking times. The later imperialist period seems less brutal to me.
Pre-agricultural societies are generally much more brutal because you need a lot of territory to feed relatively few people. Agriculturalists can conquer other people and make them work for them in a way that doesn't scale for hunters-gatherers. The consequence is that the combatant/noncombatant distinction is much more blurry, and genocide is often an explicit goal of the war.
