Steven LeBlanc thoroughly documents how our protohuman ancestors consistently over populated and exceeded their local carrying capacity. Violence to get other groups’ resources soon followed.

When we evolved into Homo sapiens, our troupes grew into tribes, then chieftains, where the battles continued on larger scales. Complex societies grew and created empires. Each one exceeded its carrying capacity until it was unable to expand further, and suffered the collapse Jared Diamond documented.

Examples from all over the planet and spanning the whole of human existence are given, driving home the point that population pressures cause war and eventually social demise from a lack of resources and ecological degradation.

Peoples of the past sought to increase their resources as efforts to maintain their populations within the carrying capacity of their environments proved inadequate.

In the final chapter, “War or Peace for the Future?” LeBlanc ignores what he has proved, and explains how this time it’s different. Rather than improving our population density, we just need more resources.

He downplays our current population growth:

Already, about 25 percent of the world’s population on a country-by-country basis is either stable or slightly declining, and the rates of most of the high-growth areas like China, India, and South America are also declining. p227

Less than 10 percent of the world’s population lives in countries where population is either stable or declining, but even 25 percent would not be significant when the other portion more than compensates. In addition, if population decline is due to out-migration, global population isn’t changed.

True, “rates of the high-growth areas” are declining, as are growth rates almost everywhere, but the human family continues to increase by more than 76 million per year.

In spite of the pronounced impact industrialized states make on the environment, their technology and slow growth rates enable them to live well below the carrying capacity. The decline in warfare among those countries is incredibly strong. p228

Only a handful of industrialized states are living below their carrying capacity, and their ecosystems’ health is not improving. Canada is supposedly below capacity, thanks to a low population density, but they are still participating in warfare over resources.

If everyone on Earth used energy, seafood, trees, and a long list of other resources at the rate Americans do, resources would be depleted far faster than they could regenerate. p229

That’s a colossal understatement. If everyone consumed as US residents, it would take resources of 3.5 Earths. An average Earthling uses the equivalent of 2.6 hectares (6.4 acres) of biologically productive land, while Earth provides 1.8 hectares (4.5 acres). Humanity is well into overshoot.

For the first time in history, technology and science enable us to understand Earth’s ecology and our impact on it, to control population growth, and to increase the carrying capacity in ways never before imagined. The opportunity for humans to live in long term balance with nature is within our grasp if we do it right. p229

Controlled population growth is still growth and it remains the driver of war, starvation, environmental degradation, and eventually collapse. Carrying capacity was increased twice in ways we never before imagined: agricultural revolution and industrial revolution. The green revolution also increased our carrying capacity, but that was easy to imagine. What wasn’t imagined was the ecological degradation and loss of long-term productivity which has resulted.

Now a new technological revolution imagined by LeBlanc and many others might increase our carrying capacity for a while, and then what?

Constant Battles ends with a summary of the evidence:

If, as I believe, warfare has ultimately been a constant battle over scarce resources throughout the ages, then only solving the problem of adequate resources will enable us to become better at ridding ourselves of conflict.

Exactly. And how shall we solve the age-old problem of inadequate resources?

For the first time in history, we have a real ability to provide adequate resources for everyone living on the planet. If we have reached a point at which we can live within Earth’s carrying capacity, we can eliminate warfare in the same way we can eliminate infectious disease: not perfectly, not immediately, but slowly and surely. p230

Once again, improving our population density doesn’t figure into the solution. Perhaps the author isn’t willing to consider our excessive breeding to be the cause of problems today, though he proves it has been for the previous six million years. If he dealt with that side of the equation, solutions would include promoting contraception and reproductive responsibility.

Maybe the publisher would only accept his book with an uplifting ending that endorses the status quo.

LeBlanc’s ignoring of his own evidence provides one more example of humanity’s unwillingness or inability to accept that our problems, and the biosphere’s problems, are caused by our excessive breeding. Rather than pursuing the futile goal of ever-increasing resources, we have the potential for eliminating warfare by decreasing our demands for those resources.