The Better Angels of Our Nature: Why Violence Has Declined is a 2011 book by Steven Pinker, in which the author argues that violence in the world has declined both in the long run and in the short run and suggests explanations as to why this has occurred. The book uses data documenting declining violence across time and geography. This paints a picture of massive declines in the violence of all forms, from war, to improved treatment of children. He highlights the role of nation-state monopolies on force, of commerce (making other people become more valuable alive than dead), of increased literacy and communication (promoting empathy), as well as a rise in a rational problem-solving orientation as possible causes of this decline in violence. He notes that paradoxically, our impression of violence has not tracked this decline, perhaps because of increased communication, and that further decline is not inevitable, but is contingent on forces harnessing our better motivations such as empathy and increases in reason.

The book's title was taken from the ending of U.S. president Abraham Lincoln's first inaugural address. Pinker uses the phrase as a metaphor for four human motivations – empathy, self-control, the "moral sense", and reason – that, he writes, can "orient us away from violence and towards cooperation and altruism."

Pinker presents a large amount of data (and statistical analysis thereof) that, he argues, demonstrate that violence has been in decline over millennia and that the present is probably the most peaceful time in the history of the human species. The decline in violence, he argues, is enormous in magnitude, visible on both long and short time scales and found in many domains including military conflict, homicide, genocide, torture, criminal justice, and treatment of children, homosexuals, animals and racial and ethnic minorities. He stresses that "The decline, to be sure, has not been smooth; it has not brought violence down to zero; and it is not guaranteed to continue."

Pinker argues that the radical declines in violent behavior that he documents do not result from major changes in human biology or cognition. He specifically rejects the view that humans are necessarily violent, and thus have to undergo radical change in order to become more peaceable. However, Pinker also rejects what he regards as the simplistic nature versus nurture argument, which would imply that the radical change must therefore have come purely from external "(nurture)" sources. Instead, he argues that: "The way to explain the decline of violence is to identify the changes in our cultural and material milieu that have given our peaceable motives the upper hand."

Pinker identifies five "historical forces" that have favored "our peaceable motives" and "have driven the multiple declines in violence". They are:

The first section of the book, chapters 2 through 7, seeks to demonstrate and to analyze historical trends related to declines of violence on different scales. Chapter 8 discusses five "inner demons" – psychological systems that can lead to violence. Chapter 9 examines four "better angels" or motives that can incline people away from violence. The last chapter examines the five historical forces listed above that have led to declines in violence.

Pinker rejects what he calls the "Hydraulic Theory of Violence" – the idea "that humans harbor an inner drive toward aggression (a death instinct or thirst for blood), which builds up inside us and must periodically be discharged. Nothing could be further from contemporary scientific understanding of the psychology of violence." Instead, he argues, research suggests that "aggression is not a single motive, let alone a mounting urge. It is the output of several psychological systems that differ in their environmental triggers, their internal logic, their neurological basis, and their social distribution." He examines five such systems:

Pinker examines four motives that can orient [humans] away from violence and towards cooperation and altruism. He identifies: