Steven Pinker opens A History of Violence with an evocative example of how things have changed over the years:
In sixteenth-century Paris, a popular form of entertainment was cat-burning, in which a cat was hoisted in a sling on a stage and slowly lowered into a fire. According to historian Norman Davies, “[T]he spectators, including kings and queens, shrieked with laughter as the animals, howling with pain, were singed, roasted, and finally carbonized.” Today, such sadism would be unthinkable in most of the world. This change in sensibilities is just one example of perhaps the most important and most underappreciated trend in the human saga: Violence has been in decline over long stretches of history, and today we are probably living in the most peaceful moment of our species’ time on earth.
(Emphasis mine.) For example:
At the widest-angle view, one can see a whopping difference across the millennia that separate us from our pre-state ancestors. Contra leftist anthropologists who celebrate the noble savage, quantitative body-counts — such as the proportion of prehistoric skeletons with axemarks and embedded arrowheads or the proportion of men in a contemporary foraging tribe who die at the hands of other men — suggest that pre-state societies were far more violent than our own. It is true that raids and battles killed a tiny percentage of the numbers that die in modern warfare. But, in tribal violence, the clashes are more frequent, the percentage of men in the population who fight is greater, and the rates of death per battle are higher. According to anthropologists like Lawrence Keeley, Stephen LeBlanc, Phillip Walker, and Bruce Knauft, these factors combine to yield population-wide rates of death in tribal warfare that dwarf those of modern times. If the wars of the twentieth century had killed the same proportion of the population that die in the wars of a typical tribal society, there would have been two billion deaths, not 100 million.
He notes two important books on violence:
Thomas Hobbes, Leviathan (1651). “And the life of man, solitary, poor, nasty, brutish, and short.” This pithy description of life in a state of nature is just one example of the lively prose in this seventeenth-century masterpiece. Hobbes’s analysis of the roots and varieties of violence is uncannily modern, and anticipated many insights from game theory and evolutionary psychology. He also was the first cognitive scientist, outlining a computational theory of memory, imagination, and reasoning.Martin Daly and Margo Wilson, Homicide (1988). This is the book that sold me on evolutionary psychology. Daly and Wilson use homicide statistics as an assay for human conflict, together with vivid accounts from history, journalism, and anthropology. They select each of the pairings of killer and victim — fratricide, filicide, parricide, infanticide, uxoricide, stepparent-stepchild, acquaintances, feuds & duels, amok killers, and so on — and test predictions from evolutionary theory on their rates and patterns. The book is endlessly insightful and beautifully written.