Is the Long Peace long enough ?

Is the decrease of nation-state conflicts since WWII due to real causes, or is it simply a statistical fluke ? Stephen Pinker favours the former, others the latter. The interviewee here also generally falls into the latter camp - or rather, he seems to think that's it's just too early to tell. The problem is that if the changes after WWII really have made war less probable, at least for the West, we still haven't had long enough to tell if this is the kind of gap that might happen anyway through chance.

If you replay the statistics of the past 200 years, you would see periods of time that are as peaceful and at least as long as this long peace. This approach is what you would call a change-point analysis, because we know when we think something changed in the history of the production of wars. Can we tell a difference between the statistics on one side of that change-point from the statistics on the other side? Looking at the sizes of wars and then separately at the rate at which they’re produced, we don’t see any evidence of a change.

I think of myself as an optimist. I look at the broader set of evidence, and I see that there are reasons to believe things are changing. The pattern appears consistent with an idea that there is a trend here—that the risk of a large war among some nations is going down in part because there has not been a large war on the European continent since World War II, a clear success of efforts to promote peace. But if those efforts really are having an impact, we may not know for a long time how big that impact is.

I don't know how detailed his investigations have been because I haven't read the paper. But I wonder if it's really so valid to model the prospect of war statistically. In any given conflict there must be many different contributing factors and variable circumstances. So if any group of nations were to enact policies that made war between them less likely, that wouldn't prevent some other external nation coming along and attacking them anyway. I imagine that it might be possible to somewhat account for this, but surely there must be so many varying effects at work it would be difficult even to say if the chance of war had really gone down or not.

What makes things so interesting is that so much has changed in the world over this 200 year period. Public health. The world population. The number of nations. Technology has revolutionized everything. A wide variety of completely crazy geopolitical events have unfolded—plenty of nastiness in terms of nations becoming more autocratic along with nations being more democratic, et cetera. And yet, evidently the statistics of war have remained stable despite the changes in either direction. Why? I don’t know. I hope somebody else will look into this and tell me what the answer is.

Well, I'm again reminded of this answer on Quora which claims it's all due to age distribution. But I haven't found the original paper, so it's hard to check the details of that. It's also worth mentioning a recent study which found that non-violent protests are much more successful at regime change than violent revolutions.

The long peaces are relatively common statistical patterns under this model just because large wars are extremely rare. Because it’s fully specified, we can use that model to ask a question about the future: If that relative decrease in war were to stick around for a much larger period of time, how many more years would it need to hold before you could really say, yes, this postwar period is different from what we would expect from a stationary model where nothing’s changed. That’s where the number of 100-140 years comes out. At that point, we can then say definitively, by only looking at the severities and frequencies of wars, that the long peace is different. If you had a more sophisticated model that included information like where wars were fought, who was fighting in them, and why, et cetera, you could maybe shrink that number to some degree.

That leaves me confused as to what the analysis actually did. If it was just looking at the frequency of wars and periods of peace, then I don't think it says anything much. Surely at the very least you have to look at which nations are fighting which nations in order to account for varying local and global effects; you could at least say if the peace between Britain and France is statistically unusual or not. Otherwise I don't see that a global analysis would tell you very much. Direct link to the paper here for anyone who wants to check (I may or may not do this, time permitting).

Why Our Postwar "Long Peace" Is Fragile - Facts So Romantic - Nautilus

You could be forgiven for balking at the idea that our post-World War II reality represents a "Long Peace." The phrase, given the prevalence of violent conflict worldwide, sounds more like how Obi-wan Kenobi might describe the period "before the dark times, before the Empire."