During war, ordinary humans routinely kill other humans. As discussed above, human beings are not natural born killers of other humans. Therefore, how do we explain human violence in war? Killing during war depends on soldiers being trained to, and developing habit of, killing on orders. Killing during war is a behavior taught to soldiers. They are taught to follow the orders of a few leaders who are themselves following the orders of their superiors. They kill on orders. The real killers are the politicians whose actions led to war.
Humans are social primates with social instincts, one of which is docility, a predisposition to obey the tribe leader and other dominant males. This resulted in fewer status fights and meant more young, unmarried males were available to protect the tribe or to hunt for food. A tribe would flourish best if it members were both aggressive towards outsiders and amenable to social control.
This process works if the tribe is kept small. However, when one person gains command of a large group of males, such as a city, war becomes possible. Due to the intense training and unquestioning obedience of the warriors, war only requires a few leaders that are murderers. Stanley Milgram in his 1974 book The Perils of Obedience described experiments that showed how otherwise ethical people could be induced to torture another person by the presence of an authority figure that commands and legitimizes the violence.