The annals of human violence include enough kinds of victims to fill a page of a rhyming dictionary: homicide, democide, genocide, ethnocide, politicide, regicide, infanticide, neonaticide, filicide, siblicide, gynecide, uxoricide, mariticide, and terrorism by suicide. Violence is found throughout the history and prehistory of our species and shows no signs of having been invented in one place and spread to the others.
At the same time, the quantitative study of history provides some pleasant surprises. Abominable customs such as human sacrifice, chattel slavery, and torture-executions for victimless crimes have been abolished. Homicide rates have plunged since the Middle Ages, and rates of battle death in armed conflict are at an all-time low. Whatever causes violence, it is not a perennial urge like hunger, sex, or the need to sleep. The historical decline of violence thereby allows us to dispatch a dichotomy that has stood in the way of understanding the roots of violence for millennia: whether humankind is basically bad or basically good, an ape or an angel, a hawk or a dove, the nasty brute of textbook Hobbes or the noble savage of textbook Rousseau. Left to their own devices, humans will not fall into a state of peaceful cooperation, but nor do they have a thirst for blood that must regularly be slaked. Human nature accommodates motives that impel us to violence, like predation, dominance, and vengeance, but also motives that -- under the right circumstances -- impel us toward peace, like compassion, fairness, self-control, and reason.
Contests for dominance, even when nothing tangible is at stake, are among the deadliest forms of human quarrel. At one end of the magnitude scale, many destructive wars have been fought over nebulous claims to national preeminence, including World War I. At the other end of the scale, the single largest motive for homicide on police blotters are "altercation of relatively trivial origin; insult, curse, jostling, etc."
There really is a commodity at stake in contests for dominance, namely information: a shared understanding of who will not back down. The socially constructed nature of dominance can help explain which individuals take risks to defend it. Perhaps the most extraordinary popular delusion about violence of the past quarter-century is that it is caused by low self-esteem. Self-esteem can be measured, and surveys show that it is the psychopaths, street toughs, bullies, abusive husbands, serial rapists, and hate-crime perpetrators who are off the scale. Psychopaths and other violent people are narcissistic: They think well of themselves not in proportion to their accomplishments but out of a congenital sense of entitlement. When reality intrudes, as it inevitably will, they treat the bad news as a personal affront, and its bearer, who is endangering their fragile reputation, as a malicious slanderer.
Violence-prone personality traits are even more consequential when they infect political rulers, because their hang-ups can affect hundreds of millions of people rather than just the unlucky few who live with them or cross their paths. Unimaginable amounts of suffering have been caused by tyrants who callously presided over the immiseration of their peoples or launched destructive wars of conquest. The Diagnostic and Statistical Manual of Mental Disorders (DSM) of the American Psychiatric Association defines narcissistic personality disorder as "a pervasive pattern of grandiosity, need for admiration, and a lack of empathy." The trio of symptoms at narcissism's core -- grandiosity, need for admiration, and lack of empathy -- fits tyrants to a T. It is most obvious in their vainglorious monuments, hagiographic iconography, and obsequious mass rallies. And with armies and police forces at their disposal, narcissistic rulers leave their mark in more than statuary; they can authorize vast outlays of violence. As with garden-variety bullies and toughs, the unearned self-regard of tyrants is eternally vulnerable to being popped, so any opposition to their rule is treated not as a criticism but as a heinous crime. At the same time, their lack of empathy imposes no brake on the punishment they mete out to real or imagined opponents. Nor does it allow any consideration of the human costs of another of their DSM symptoms: their "fantasies of unlimited success, power, brilliance, beauty, or ideal love," which may be realized in rapacious conquest, pharaonic construction projects, or utopian master plans.