About That Apparent Decline in Violent Conflict…

Is violent conflict declining, or isn’t it? I’ve written here and elsewhere about evidence that warfare and mass atrocities have waned significantly in recent decades, at least when measured by the number of people killed in those episodes. Not everyone sees the world the same way, though. Bear Braumoeller asserts that, to understand how war prone the world is, we should look at how likely countries are to use force against politically relevant rivals, and by this measure the rate of warfare has held pretty steady over the past two centuries. Tanisha Fazal argues that wars have become less lethal without becoming less frequent because of medical advances that help keep more people in war zones alive. Where I have emphasized war’s lethal consequences, these two authors emphasize war’s likelihood, but their arguments suggest that violent conflict hasn’t really waned the way I’ve alleged it has.

This week, we got another important contribution to the wider debate in which my shallow contributions are situated. In an updated working paper, Pasquale Cirillo and Nassim Nicholas Taleb claim to show that

Violence is much more severe than it seems from conventional analyses and the prevailing “long peace” theory which claims that violence has declined… Contrary to current discussions…1) the risk of violent conflict has not been decreasing, but is rather underestimated by techniques relying on naive year-on-year changes in the mean, or using sample mean as an estimator of the true mean of an extremely fat-tailed phenomenon; 2) armed conflicts have memoryless inter-arrival times, thus incompatible with the idea of a time trend.

Let me say up front that I only have a weak understanding of the extreme value theory (EVT) models used in Cirillo and Taleb’s paper. I’m a political scientist who uses statistical methods, not a statistician, and I have neither studied nor tried to use the specific techniques they employ.

Bearing that in mind, I think the paper successfully undercuts the most optimistic view about the future of violent conflict—that violent conflict has inexorably and permanently declined—but then I don’t know many people who actually hold that view. Most of the work on this topic distinguishes between the observed fact of a substantial decline in the rate of deaths from political violence and the underlying risk of those deaths and the conflicts that produce them. We can (partly) see the former, but we can’t see the latter; instead, we have to try to infer it from the conflicts that occur. Observed history is, in a sense, a single sample drawn from a distribution of many possible histories, and, like all samples, this one is only a jittery snapshot of the deeper data-generating process in which we’re really interested. What Cirillo and Taleb purport to show is that long sequences of relative peace like the one we have seen in recent history are wholly consistent with a data-generating process in which the risk of war and death from it have not really changed at all.

Of course, the fact that a decades-long decline in violent conflict like the one we’ve seen since World War II could happen by chance doesn’t necessarily mean that it is happening by chance. The situation is not dissimilar to one we see in sports when a batter or shooter seems to go cold for a while. Oftentimes that cold streak will turn out to be part of the normal variation in performance, and the athlete will eventually regress to the mean—but not every time. Sometimes, athletes really do get and stay worse, maybe because of aging or an injury or some other life change, and the cold streak we see is the leading edge of that sustained decline. The hard part is telling in real time which process is happening. To try to do that, we might look for evidence of those plausible causes, but humans are notoriously good at spotting patterns where there are none, and at telling ourselves stories about why those patterns are occurring that turn out to be bunk.

The same logic applies to thinking about trends in violent conflict. Maybe the downward trend in observed death rates is just a chance occurrence in an unchanged system, but maybe it isn’t. And, as Andrew Gelman told Zach Beauchamp, the statistics alone can’t answer this question. Cirillo and Taleb’s analysis, and Braumoeller’s before it, imply that the history we’ve seen in the recent past  is about as likely as any other, but that fact isn’t proof of its randomness. Just as rare events sometimes happen, so do systemic changes.

Claims that “This time really is different” are usually wrong, so I think the onus is on people who believe the underlying risk of war is declining to make a compelling argument about why that’s true. When I say “compelling,” I mean an argument that a) identifies specific causal mechanisms and b) musters evidence of change over time in the presence or prevalence of those mechanisms. That’s what Steven Pinker tries at great length to do in The Better Angels of Our Nature, and what Joshua Goldstein did in Winning the War on War.

My own thinking about this issue connects the observed decline in the the intensity of violent conflict to the rapid increase in the past 100+ years in the size and complexity of the global economy and the changes in political and social institutions that have co-occurred with it. No, globalization is not new, and it certainly didn’t stop the last two world wars. Still, I wonder if the profound changes of the past two centuries are accumulating into a global systemic transformation akin to the one that occurred locally in now-wealthy societies in which organized violent conflict has become exceptionally rare. Proponents of democratic peace theory see a similar pattern in the recent evidence, but I think they are too quick to give credit for that pattern to one particular stream of change that may be as much consequence as cause of the deeper systemic transformation. I also realize that this systemic transformation is producing negative externalities—climate change and heightened risks of global pandemics, to name two—that could offset the positive externalities or even lead to sharp breaks in other directions.

It’s impossible to say which, if any, of these versions is “true,” but the key point is that we can find real-world evidence of mechanisms that could be driving down the underlying risk of violent conflict. That evidence, in turn, might strengthen our confidence in the belief that the observed pattern has meaning, even if it doesn’t and can’t prove that meaning or any of the specific explanations for it.

Finally, without deeply understanding the models Cirillo and Taleb used, I also wondered when I first read their new paper if their findings weren’t partly an artifact of those models, or maybe some assumptions the authors made when specifying them. The next day, David Roodman wrote something that strengthened this source of uncertainty. According to Roodman, the extreme value theory (EVT) models employed by Cirillo and Taleb can be used to test for time trends, but the ones described in this new paper don’t. Instead, Cirillo and Taleb specify their models in a way that assumes there is no time trend and then use them to confirm that there isn’t. “It seems to me,” Roodman writes, “that if Cirillo and Taleb want to rule out a time trend according to their own standard of evidence, then they should introduce one in their EVT models and test whether it is statistically distinguishable from zero.”

If Roodman is correct on this point, and if Cirillo and Taleb were to do what he recommends and still find no evidence of a time trend, I would update my beliefs accordingly. In other words, I would worry a little more than I do now about the risk of much larger and deadlier wars occurring again in my expected lifetime.

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A Note on Trends in Armed Conflict

In a report released earlier this month, the Project for the Study of the 21st Century (PS21) observed that “the body count from the top twenty deadliest wars in 2014 was more than 28% higher than in the previous year.” They counted approximately 163 thousand deaths in 2014, up from 127 thousand in 2013. The report described that increase as “part of a broader multi-year trend” that began in 2007. The project’s executive director, Peter Epps, also appropriately noted that “assessing casualty figures in conflict is notoriously difficult and many of the figures we are looking at here a probably underestimates.”

This is solid work. I do not doubt the existence of the trend it identifies. That said, I would also encourage us to keep it in perspective:

That chart (source) ends in 2005. Uppsala University’s Department of Peace and Conflict (UCDP) hasn’t updated its widely-used data set on battle-related deaths for 2014 yet, but from last year’s edition, we can see the tail end of that longer period, as well as the start of the recent upward trend PS21 identifies. In this chart—R script here—the solid line marks the annual, global sums of their best estimates, and the dotted lines show the sums of the high and low estimates:
Annual, global battle-related deaths, 1989-2013 (source: UCDP)

Annual, global battle-related deaths, 1989-2013 (Data source: UCDP)

If we mentally tack that chart onto the end of the one before it, we can also see that the increase of the past few years has not yet broken the longer spell of relatively low numbers of battle deaths. Not even close. The peak around 2000 in the middle of the nearer chart is a modest bump in the farther one, and the upward trend we’ve seen since 2007 has not yet matched even that local maximum. This chart stops at the end of 2013, but if we used the data assembled by PS21 for the past year to project an increase in 2014, we’d see that we’re still in reasonably familiar territory.

Both of these things can be true. We could be—we are—seeing a short-term increase that does not mark the end of a longer-term ebb. The global economy has grown fantastically since the 1700s, and yet it still suffers serious crises and recessions. The planet has warmed significantly over the past century, but we still see some unusually cool summers and winters.

Lest this sound too sanguine at a time when armed conflict is waxing, let me add two caveats.

First, the picture from the recent past looks decidedly worse if we widen our aperture to include deliberate killings of civilians outside of battle. UCDP keeps a separate data set on that phenomenon—here—which they label “one-sided” violence. If we add the fatalities tallied in that data set to the battle-related ones summarized in the previous plot, here is what we get:

Annual, global battle-related deaths and deaths from one-sided violence, 1989-2013 (Data source: UCDP)

Annual, global battle-related deaths and deaths from one-sided violence, 1989-2013 (Data source: UCDP)

Note the difference in the scale of the y-axis; it is an order of magnitude larger than the one in the previous chart. At this scale, the peaks and valleys in battle-related deaths from the past 25 years get smoothed out, and a single peak—the Rwandan genocide—dominates the landscape. That peak is still much lower than the massifs marking the two World Wars in the first chart, but it is huge nonetheless. Hundreds of thousands of people were killed in a matter of months.

Second, the long persistence of this lower rate does not prove that the risk of violent conflict on the scale of the two World Wars has been reduced permanently. As Bear Braumoeller (here) and Nassim Nicholas Taleb (here; I link reluctantly, because I don’t care for the scornful and condescending tone) have both pointed out, a single war between great powers could end or even reverse this trend, and it is too soon to say with any confidence whether or not the risk of that happening is much lower than it used to be. Like many observers of international relations, I think we need to see how the system processes the (relative) rise of China and declines of Russia and the United States before updating our beliefs about the risk of major wars. As someone who grew up during the Cold War and was morbidly fascinated by the possibility of nuclear conflagration, I think we also need to remember how close we came to nuclear war on some occasions during that long spell, and to ponder how absurdly destructive and terrible that would be.

Strictly speaking, I’m not an academic, but I do a pretty good impersonation of one, so I’ll conclude with a footnote to that second caveat: I did not attribute the idea that the risk of major war is a thing of the past to Steven Pinker, as some do, because as Pinker points out in a written response to Taleb (here), he does not make precisely that claim, and his wider point about a long-term decline in human violence does not depend entirely on an ebb in warfare persisting. It’s hard to see how Pinker’s larger argument could survive a major war between nuclear powers, but then if that happened, who would care one way or another if it had?

Whither Organized Violence?

The Human Security Research Group has just published the latest in its series of now-annual reports on “trends in organized violence around the world,” and it’s essential reading for anyone deeply interested in armed conflict and other forms of political violence. You can find the PDF here.

The 2013 edition takes Steven Pinker’s Better Angels as its muse and largely concurs with Pinker’s conclusions. I’ll sheepishly admit that I haven’t read Pinker’s book (yet), so I’m not going to engage directly in that debate. Instead, I’ll call attention to what the report’s authors infer from their research about future trends in political violence. Here’s how that bit starts, on p. 18:

The most encouraging data from the modern era come from the post–World War II years. This period includes the dramatic decline in the number and deadliness of international wars since the end of World War II and the reversal of the decades-long increase in civil war numbers that followed the end of the Cold War in the early 1990s.

What are the chances that these positive changes will be sustained? No one really knows. There are too many future unknowns to make predictions with any degree of confidence.

On that point, political scientist Bear Braumoeller would agree. In an interview last year for Popular Science (here), Kelsey Atherton asked Braumoeller about Braumoeller’s assertion in a recent paper (here) that it will take 150 years to know if the downward trend in warfare that Pinker and others have identified is holding. Braumoeller replied:

Some of this literature points to “the long peace” of post-World War II. Obviously we haven’t stopped fighting wars entirely, so what they’re referring to is the absence of really really big wars like World War I and World War II. Those wars would have to be absent for like 70 to 75 more years for us to have confidence that there’s been a change in the baseline rate of really really big wars.

That’s sort of a separate question from how we know whether there are trends in warfare in general. We need to understand that war and peace are both stochastic processes. We need a big enough sample to rule out the historical average, which is about one or two big wars per century. We just haven’t had enough time since World War I and World War II to rule out the possibility that nothing’s changed.

I suspect that the authors of the Human Security Report would not dispute that claim, but after carefully reviewing Pinker’s and their own evidence, they do see causes for cautious optimism. Here I’ll quote at length, because I think it’s important to see the full array of forces taken into consideration to increase our confidence in the validity of the authors’ cautious speculations.

The case for pessimism about the global security future is well rehearsed and has considerable support within the research community. Major sources of concern include the possibility of outbreaks of nuclear terrorism, a massive transnational upsurge of lethal Islamist radicalism, or wars triggered by mass droughts and population movements driven by climate change.

Pinker notes reasons for concern about each of these potential future threats but also skepticism about the more extreme claims of the conflict pessimists. Other possible drivers of global violence include the political crises that could follow the collapse of the international financial system and destabilizing shifts in the global balance of economic and military power—the latter being a major concern of realist scholars worried about the economic and military rise of China.

But focusing exclusively on factors and processes that may increase the risks of large-scale violence around the world, while ignoring those that decrease it, also almost certainly leads to unduly pessimistic conclusions.

In the current era, factors and processes that reduce the risks of violence not only include the enduring impact of the long-term trends identified in Better Angels but also the disappearance of two major drivers of warfare in the post–World War II period—colonialism and the Cold War. Other post–World War II changes that have reduced the risks of war include the entrenchment of the global norm against interstate warfare except in self-defence or with the authority of the UN Security Council; the intensification of economic and financial interdependence that increases the costs and decreases the benefits of cross-border warfare; the spread of stable democracies; and the caution-inducing impact of nuclear weapons on relations between the major powers.

With respect to civil wars, the emergent and still-growing system of global security governance discussed in Chapter 1 has clearly helped reduce the number of intrastate conflicts since the end of the Cold War. And, at what might be called the “structural” level, we have witnessed steady increases in national incomes across the developing world. This is important because one of the strongest findings from econometric research on the causes of war is that the risk of civil wars declines as national incomes—and hence governance and other capacities—increase. Chapter 1 reports on a remarkable recent statistical study by the Peace Research Institute, Oslo (PRIO) that found that if current trends in key structural variables are sustained, the proportion of the world’s countries afflicted by civil wars will halve by 2050.

Such an outcome is far from certain, of course, and for reasons that have yet to be imagined, as well as those canvassed by the conflict pessimists. But, thanks in substantial part to Steven Pinker’s extraordinary research, there are now compelling reasons for believing that the historical decline in violence is both real and remarkably large—and also that the future may well be less violent than the past.

After reading the new Human Security Report, I remain a short-term pessimist and long-term optimist. As I’ve said in a few recent posts (see especially this one), I think we’re currently in the thick of period of systemic instability that will continue to produce mass protests, state collapse, mass killing, and other forms of political instability at higher rates than we’ve seen since the early 1990s for at least the next year or two.

At the same time, I don’t think this local upswing marks a deeper reversal of the long-term trend that Pinker identifies, and that the Human Security Report confirms. Instead, I believe that the global political economy is continuing to evolve in a direction that makes political violence less common and less lethal. This system creep is evident not only in the aforementioned trends in armed violence, but also in concurrent and presumably interconnected trends in democratization, socio-economic development, and global governance. Until we see significant and sustained reversals in most or all of these trends, I will remain optimistic about the directionality of the underlying processes of which these data can give us only glimpses.

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