Excellent book although pretty heavy on psychology and brain functions. It describes the progression of human behavior, especially of people in Europe, from the Middle Ages to the present. Let's face it -- Europeans in the Middle Ages were pretty gross and crude, not to mention intolerant, murderous, and with disgusting personal hygiene. They delighted in torturing fellow humans and animals for entertainment, murdering Jews, burning women accused of being witches, practicing slavery, and executing people for hundreds of relatively insignificant "crimes."
A key point of the book is that ten thousand years ago, perhaps one person in four died of violence. Today, it is more like one person in 10,000 world wide and perhaps one person in a hundred thousand in the the modern-day EU. The author also discusses the outlier US behavior, with a homicide rate that is eight times that in the EU.
Another very good book on a related subject is "WAR! What Is It Good For? Conflict and the Progress of Civilization from Primates to Robots" by Morris (2014).