People wage war on each other because they want to protect something - their lives, their resources, their families, their beliefs - as all of this is to some degree a part of them or they depend on them, thus part of survival instinct. Without that survival instinct, we would've gone extinct long ago. Without that protection instinct, we couldn't have built societies. So the underlying motivations of war, from self-defense to greed, all root in very basic subconscious human impulses.
As long as survival instinct favors the individual (first priority) and its group (second priority) over "foreigners", empathy with possible victims will probably not be enough to prevent a war with high enough success rating.