From pages of 55-56 of The Better Angels of our Nature:
…the murder rate of the [modern hunter-gatherer] !Kung went down by a third after their territory has been brought under the control of Botswana government, as the Leviathan theory would predict.
The reduction of homicide by government control is so obvious to anthropologists that they seldom document it with numbers. The various “paxes” that one reads about in history books – the Paw Romana, Islamica, Mongolica, Hispanica, Ottomana, Sinica, Britannica, Australiana (in New Guinea), Canadiana (in the Pacific Northwest), and Praetoriana (in South Africa) – refer to the reduction in raiding, feuding, and warfare in the territories brought under the control of an effective government.
Though imperial conquest and rule can themselves be brutal, they do reduce endemic violence among the conquered. The Pacification Process is so pervasive that anthropologists often treat it as a methodological nuisance. It goes without saying that peoples that have been brought under the jurisdication of a government will not fight as much, so they are simply excluded from studies of violence in indigenous societies. The effect is also noticeable to the people themselves. As an Auyana man living in New Guinea under the Pax Australiana put it, “Life was better since the government came” because “a man could now eat without looking over his should and could leave his house in the morning to urinate without fear of being shot.”
The anthropologists Karen Ericksen and Heather Horton have quantified the way that the presence of government can move a society away from lethal vengeance. In a survey of 192 traditional societies, they found that one-on-one revenge was common in foraging societies, and kin0against0kin blood feuds were common in tribal societies that had not been pacified by a colonial or national government, particularly if they had an exaggerated culture of manly honor. Adjudication by tribunals and courts, in contrast, was common in societies that had fallen under the control of a centralized government, or that had resource bases and inheritance patterns that gave people more of a stake in social stability.
Not a naive statist, Pinker concludes this chapter two pages later by saying,
When it came to violence, then, the first Leviathan solved one problems but created another. People were less likely to become victims of homicide or casualties of war, but they were now under the thumbs of tyrants, clerics, and kleptocrats. This gives us the more sinister sense of the word pacification: not just bringing about peace but the imposition of absolute control by a coercive government. Solving this second problem would have to wait another few millennia, and in much of the world it remains unsolved to this day.