In the book, Keeley aims to stop the apparent trend in seeing modern civilization as bad, by setting out to prove that prehistoric societies were often violent and engaged in frequent warfare that was highly destructive to the cultures involved.

[3] Nicholas Wade writes: "Had the same casualty rate been suffered by the population of the twentieth century, its war deaths would have totaled two billion people.

[5] One-half of the people found in a mesolithic cemetery in present-day Jebel Sahaba, Sudan dating to as early as 13,000 years ago had died as a result of warfare between seemingly different racial groups with victims bearing marks of being killed by arrow heads, spears and club, prompting some to call it the first race war.

[6][7] The Yellowknives tribe in Canada was effectively obliterated by massacres committed by Dogrib Indians, and disappeared from history shortly thereafter.

Iroquois routinely slowly tortured to death captured enemy warriors (see Captives in American Indian Wars for details).

For example, the large pueblo at Sand Canyon in Colorado, although protected by a defensive wall, was almost entirely burned, artifacts in the rooms had been deliberately smashed, and bodies of some victims were left lying on the floors.

Indigenous groups in many areas of the world successfully defended and defeated multiple European colonization campaigns for decades due to primitive unorthodox warfare techniques like smaller mobile units, using small arms as opposed to artillery, open formations, frequent uses of ambushes and raids, surprise attacks, destruction of infrastructure (e.g. villages, habitations, foodstores, livestock, means of transportation), extensive uses of scouts.

Keeley relates an incident in which an Eipo tribal leader of highland Irian (in Western New Guinea) quickly thought of – and wanted to immediately use – aerial bombardment of enemies shortly after seeing an airplane for the first time.

The New York Times said that "the book's most dramatic payoff is its concluding explanation for the recent "pacification of the past" by scholars"[12] and that "...revulsion with the excesses of World War II has led to a loss of faith in progress and Western civilization....".

American political scientist Eliot A. Cohen described the book as "At once scholarly and lucid, he paints a dark picture of human nature, although he does not believe humankind is doomed to a perpetual striving for mutual extinction.

[15] On page 93 Keeley wrote: "One author has very liberally estimated that more than 100 million people have died from all war-related causes (including famine and disease) on our planet during this century.