The war abolitionists of the 1920s Outlawry movement would have loved this book, would have seen it as a proper extension of the ongoing campaign to rid the world of war. But it is a different book from theirs. It does not preach the immorality of war. That idea, although proved truer than ever by the two world wars, failed to prevent the two world wars. When an idea's time has come and also gone, it becomes necessary to prove to people that the idea wasn't rendered impossible or naïve by "human nature" or grand forces of history or any other specter. Horgan, in exactly the approach required, preaches the scientific observation of the success (albeit incomplete as yet) of preaching the immorality of war.

The evidence, Horgan argues, shows that war is a cultural contagion, a meme that serves its own ends, not ours (except for certain profiteers perhaps). Wars happen because of their cultural acceptance and are avoided by their cultural rejection. Wars are not created by genes or avoided by eugenics or oxytocin, driven by an ever-present minority of sociopaths or avoided by controlling them, made inevitable by resource scarcity or inequality or prevented by prosperity and shared wealth, or determined by the weaponry available. All such factors, Horgan finds, can play parts in wars, but the decisive factor is a militaristic culture, a culture that glorifies war or even just accepts it, a culture that fails to renounce war as something as barbaric as cannibalism. War spreads as other memes spread, culturally. The abolition of war does the same.

Those who believe that war is in our genes or mandated by overpopulation or for whatever other reason simply unavoidable or even desirable will not be attracted to Horgan's book. But they should read it. It is written for them and carefully argued and documented. Those who, in contrast, believe it is as obvious as breathing air that we can choose to end war tomorrow will find a little sad comedy in the fact that the way we get people to choose to end a long-established institution is by rigorously persuading them that such choices have been made before and are already well underway. Yet, that is exactly what people need to hear, especially those who are on the edge between "War is in DNA" and "War is over if you want it." Most human cultures never produced nuclear bombs or genetically engineered corn or Youtube. Many cultures have produced peace. But what if they hadn't? How in the world would that prevent us from producing it?

Evidence of lethal group violence does not go back through our species' millions of years but only through the past 10,000 to 13,000. Even chimpanzees' supposed innate war spirit is not established. We are not the only primates who seem able to learn either war or peace. Annual war-related casualties have dropped more than ten-fold since the first half of the twentieth century. Democracy is no guarantee of peace, but it is allowing people to say no to war. Of course, democracy is not all or nothing. Some democracies, like ours in the United States, can be very weak, and weaker still on the question of war. What allows nations' leaders to take countries into war, Horgan shows, is not people's aggressiveness but their docility, their obedience, their willingness to follow and even to believe what authorities tell them.

Mistaken theories about the causes of war create the self-fulfilling expectation that war will always be with us. Predicting that climate change will produce world war may actually fail to inspire people to buy solar panels, inspiring them instead to support military spending and to stock up at home on guns and emergency supplies.

I wish Horgan had looked more at the motivations of those in power who choose war, some of whom do profit from it in various ways. I also think he understates the importance of the military industrial complex, whose influence Eisenhower accurately predicted would be total and even spiritual. It's harder to work for the abolition of war when the war industry is behind your job. I think this book could benefit from recognition of the U.N. Charter's limitations as compared with the Kellogg-Briand Pact, in its acceptance of wars that are either "defensive" or authorized by the United Nations. I think Horgan's view of the Arab Spring and the Libyan War is confused, as he thinks in terms of intervention in countries where the United States had already long been intervened, and he frames the choices as war or nothing. I think the final chapter on free will is rather silly, confusing the philosophical point of physical determinism with how things look from our perspective, a confusion that David Hume straightened out quite a while ago.

But Horgan makes a key point in that last chapter, pointing to a study that found that when people were exposed to the idea that they had no free will they behaved less morally, choosing to behave badly, of course, with the very same free will they nonetheless maintained. Being free to choose, we can in fact choose things that most of us never dare imagine. Here's John Horgan's perfect prescription:

"We could start by slashing our bloated military, abolishing arms sales to other countries, and getting rid of our nuclear arsenal. These steps, rather than empty rhetoric, will encourage other countries to demilitarize as well."

Or as Jean Paul Sartre put it—(Look, ma, no research!)—"To say that the for-itself has to be what it is, to say that it is what it is not while not being what it is, to say that in it existence precedes and conditions essence or inversely according to Hegel, that for it 'Wesen ist was gewesen ist'—all this is to say one and the same thing: to be aware that man is free."