When two tribes have boundaries with each other we can be almost certain that there will be killings. We are killing machine. This is in our genes.
Therefore we need to think of this as default and be proactive in minimizing amount of violence or situations that something may go wrong. Perhaps creatining institutions or organizations that minimize this.
In most animals proactive and reactive agression goes hand in hand. We are high on proactive agression (planned external agression on other tribes, nationes) and low on reactive agression (we are not aggresive to each other)
This in turn is connected to the important shift that happened in way human organize. Coalition of beta male dethroned one alpha male.
We are pathriacal society de facto. Descended from the beta males that are ruling the society. There is a lot bigger punishments for adultery, killing spouse (for woman than man)