Human beings die and kill in order to establish the truth: to prove the reality of the sacred ideal that constitutes the foundation of their society. The essence of human violence has nothing to do with biology or survival. On the country, human  violence is how we establish or reaffirm our spirituality: devotion to an abstract entity--that "thing" which the group worships in common.

The nature of the entity or idea for which human beings die and kill is fungible. Each society has their own "favorite." This is the good-old principle of "cultural relativity" that many forget in their passion to affirm their own sacred ideal.

I too may have a "favorite." But as a scientist my responsibility is to define or identify the mechanism that human beings employ to prove the truth of their  own favorite: the "beloved object" that holds their society together.

Just a few of the ideas or entities for which people have died in great numbers:

The mechanism is the same, regardless of the nature of the idea or entity: death--and memorials erected in the name of those who have died—testify to the reality of the entity or ideal. Death and memorialization perform a validation function.

And by the way, the idea of "aggression" is a smokescreen--functioning in the name of repression--negation of the truth. Pretending that the "hero" is masculine and heroic in order to deny the reality: that his role is obedience and masochistic submission. As Carolyn Marvin puts it, "We turn men into aggressive warriors so that we can kill them more easily."