Bayesian Investor Blog

Book review: The Causes of War and the Spread of Peace: But Will War Rebound?, by Azar Gat.

This book provides a good synthesis of the best ideas about why wars happen.

It overlaps a good deal with Pinker’s The Better Angels of Our Nature. Pinker provides much more detailed evidence, but Gat has a much better understanding than Pinker of the theories behind the trends.

War among hunter-gatherers

Gat starts with a thorough discussion of the evolutionary roots of war, providing clear models of how violence could have benefited those who started it in primitive environments.

He ridicules the belief that hunter-gatherers were peaceful, claiming that advocates of that position have mostly given up on defending it for the humans that were around at the start of the agricultural revolution, and have retreated to defending it for substantially earlier humans, for whom there’s less evidence available.

Gat resurrects a good deal of relevant evidence about Australian aborigines, who were pretty clearly violent when first contacted by Europeans. Those reports were mostly forgotten in recent debates on this subject, apparently just because there hadn’t been anything new to say about them for a long time.

Gat doesn’t say much about reports of peaceful bonobos, so I’ll mention the recent book that reportedly demolishes this myth.

These evolutionary considerations don’t tell us much about the future of war. They merely describe some constraints on the models we can use to do so.

Modernity

There has been a big decline in the frequency of war, which Gat says started around 1815. I.e. it coincided somewhat closely with the industrial revolution.

There were lots of changes associated with the industrial revolution, but the obvious place to start is the increase in wealth.

Gat is fairly confident that costs of war haven’t changed enough to explain why people became more averse to war. He says that what’s changed most is that the benefits of peace increased significantly with increasing wealth. He doesn’t document the benefits of peace as well as I’d like, but it seems pretty plausible that people had more options starting around 1815 for getting power/wealth via business.

Why does Gat emphasize wealth rather than democracy or capitalism?

There’s been a pretty good correlation between democracy and peace since about 1815, which is roughly the time period for which we have a good dataset to feed into our statistical models. But Gat points out that before 1815, there was approximately no reason to suspect that democracies were more peaceful than the alternatives. That seems like a pretty compelling argument against the standard “democracy causes peace” model.

It’s a bit harder to disentangle the effects of capitalism and free trade from the effects of wealth, good infrastructure, and other measures of modernity. Gat refutes the idea that peace is a simple result of the amount of trade between nations, but that seems like a bit of a straw man. The more sophisticated versions of the “trade causes peace” model seem hard to distinguish from Gat’s wealth/modernity model.

Gat reports a study which shows that modernized nations have never waged war with each other. He contrasts that to measures based on democracy and capitalism, where he points out exceptions such as democracies Greece and Turkey fighting in 1986, and capitalist Israel and Jordan fighting many times. But these claims use somewhat arbitrary classifications (e.g. Israel was modernized in 1971 but not in 1967), and Gat doesn’t ask us to put much weight on this kind of evidence.

The sexual revolution

It’s easy to forget how normal it used to be for soldiers to rape the people they conquer, enough so that becoming a soldier could easily have increased a young man’s chances of getting sex. (Young men also get sex by returning home as war heroes; it’s less clear whether changes in that effect explain long term trends in war).

That changed dramatically in the developed world about a half century ago, when the sexual revolution created conditions under which it no longer made much sense for a young man to want war. “Make love, not war” may not have described a deliberate choice that people were making, but people must have had some awareness that these used to be competing strategies to achieve sexual goals. (There was also some change in how much governments condoned rape by their soldiers. I presume this trend started before the sexual revolution, but I’m unclear about when and why that trend happened).

There are some signs that the sexual revolution was followed by an unusually large decline of war, but Gat doesn’t pay much attention to this evidence, presumably because the evidence is noisy and is similar to what he’d expect from wealth effects alone.

There’s stronger evidence that war is correlated with the proportion of the population that consists of young males, but it’s hard to say how much of that effect is due to sexual motives.

The future of war

Gat’s outlook is cautiously optimistic. Increasing wealth, increasing availability of sex, and better demographics all suggest a more peaceful future.

China and Iran are somewhat dangerous for the near future, due to having many young men (and a large gender imbalance in China), but their increasing wealth and aging demographics should reduce that risk substantially in a few decades.

Read Pinker if you want evidence about war, but read Gat if you want a clear causal model.