Does the arc of history not bend toward justice after all?

A great deal of popular research in recent years has suggested that the world is becoming more peaceful — that it is experiencing fewer devastating wars, and fewer civilians are dying in the conflicts that do break out. That idea is intrinsically appealing, because it suggests that people today are perhaps more civilized, or at least less violent, than in previous generations.

But now a new paper suggests that research could be wrong. It argues that what looked like a decline in war was actually just a statistical blip — a gap between major wars, rather than the end of them.

So which side is right? Can we carry on with our lives, secure in the knowledge that the world is becoming more peaceful? Or do we need to start worrying that we all might die in a fiery nuclear holocaust after all?

Why this is important

When Steven Pinker's book The Better Angels of Our Nature came out in 2011, it made a huge splash. Its argument — that we're living through the most peaceful era in human history — was surprising to a lot of people, given the conflicts currently being fought all over the globe, but Pinker's data seemed extremely persuasive. According to his analysis, the rate of deaths from war has reached an astonishing historical low. His theory is very appealing. Who wouldn't want to believe that we are living in a safer world, and that the future will likely be even safer?

A key part of Pinker's work is the notion of the "long peace" — an idea that Pinker actually borrows from a historian, John Lewis Gaddis. It refers to the fact that in the past 70 years, wars between great powers have basically gone away. Because situations like the Cold War never escalated to direct conflict, we've managed to avoid the type of warfare that devastated societies in the early 20th century and, indeed, much of human history.

If the causes of that are, as Pinker suggested in a lecture, "the pacifying forces" of "democracy, trade, and international society," then we should expect this trend to continue. So long as we continue to maintain the trends of the world we live in, including growing international trade, strengthening of international institutions like the UN, and strong diplomatic ties between democratic states, then we might actually be able to keep making the world a better place.

Enter NYU professor Nassim Nicholas Taleb, who is best known as the author of The Black Swan, a book on rare events. He thinks all of this is starry-eyed nonsense. In his opinion, proponents of the "war is declining" argument are over-interpreting evidence of a good trend in the same way people used to argue that the stock market could go up forever without crashes. He wrote a stinging critique of Pinker's work, which Pinker replied to, and then Taleb replied to again.

Taleb's new paper, co-authored with Delft University's Pasquale Cirillo, is the latest volley in that ongoing intellectual war. It's probably the most statistically sophisticated argument to date that war isn't declining — and that we're still every bit at risk of a major conflict as we always were.

Why Taleb and Cirillo believe the raw numbers are misleading

Taleb and Cirillo's core argument is that looking at raw numbers alone — casualty counts from different wars — is misleading. In order to understand the actual risk of large wars over time, they argue, you need some more complex statistical tools. Their paper uses a method called "extreme value theory": a type of statistical analysis specifically designed to assess the probability of rare but extremely significant events, such as a world war.

Taleb and Cirillo conclude that there are two major flaws in Pinker's theory. The first is that their analysis suggests huge conflicts (on the scale of 10 million casualties) only happen once a century, but Pinker's "long peace" only covers 70 years. That could mean that what looks like a decline in violent conflict is merely a gap between major wars.

They also conclude that Pinker has underestimated the actual average casualty numbers in major wars by about three times, and that the real numbers don't actually show a decline over time. If that's right, his measurements of the apparent decline of war are overly rosy.

For those reasons, Taleb and Cirillo argue, Pinker and his fellow optimists are wrong. Viewed through their application of extreme value theory, the decline in war looks like a myth.

So is war declining, or not?

So who is right? Is there really any reason to think that the decline in war we're seeing today is something different — or just another statistical blip before the next huge war?

Even if you think Cirillo and Taleb get the math right — which not all experts do — their paper doesn't resolve that question. It "shows that we can't infer that the risk has changed, but at the same time, it doesn't prove that it hasn't changed," explained Jay Ulfelder, an expert on statistical assessments of political violence.

Andrew Gelman, a statistician at Columbia University, says that the real problem is "somewhat extrastatistical": it's about things about the world that can't just be measured with big-picture numbers. Most importantly, we can't know whether the extraordinary peacefulness of the past 70 years is a continuing trend without really understanding why there have been so few deaths from war recently.

Pinker believes the "why" evidence is in his favor. He points to the fact that it's not just war that's declining: many other types of violence, ranging from murder to legal slavery, have been on the decline for centuries. Moreover, there are all sorts of reasons to think we've seen a revolution in human affairs in the past 200 years or so: the massive rise in global GDP, the unprecedented spread of democracy, and rapid globalization might all have altered the world in significant ways.

But the key word there is "might." This debate is far from over. Hopefully it will be resolved in the pages of academic journals — not on the battlefield.

Watch: Three big reasons war is going away