Trends over Time in State-Sponsored Mass Killing

UPDATE: After posting this on July 25, I discovered some version-related bugs in the R script used to generate the maps and animate them. I fixed those bugs in the public script on Github (see below) and generated a new version of the animation that runs through 2012.

As part of the work I’m doing for the U.S. Holocaust Memorial Museum’s Center for the Prevention of Genocide, I’m scheduled to present a paper at next month’s Annual Meeting of the American Political Science Association on an ensemble of statistical models that can be used to assess countries’ risks of state-sponsored mass killing. I plan to post the paper and associated data and code soon in an attempt to vet the work I’ve already done and to catalyze new work on the topic by other researchers. In the meantime, I thought I would post some visualizations of the historical data on episodes of state-sponsored mass killing in hopes of piquing peoples’ curiosity about this subject and the early-warning system we’re developing.

The data set I’m using for this project is based on one that Dartmouth’s Ben Valentino created for the Political Instability Task Force several years ago. I’ve written an R script that puts the published list version of Ben’s data—see the appendix to this paper—into the usual country-year format and, in consultation with Ben, extends the data through 2012. Of course, I am solely responsible for the results. You can download the country-year data in .csv format from my Google Drive, here.

For purposes of that PITF project, Ben defined a mass killing as any episode in which the actions of state agents result in the intentional death of at least 1,000 noncombatants from a discrete group in a period of sustained violence. Mass killing episodes are considered to have begun in the first year in which at least 100 intentional noncombatant fatalities occur. If fewer than 100 total fatalities are recorded annually for any three consecutive years during the episode, the episode is considered to have ended during the first year within that three-year run, even if killings continue at lower levels in later years. If the state were to resume killing more than 100 civilians per year from that same group and that new wave of killings eventually produced more than 1,000 deaths in total, that resumption would be identified as a new onset.

The stack of charts below shows trends over time in episodes of state-sponsored mass killing by looking at 1) annual counts of onsets, 2) annual rates of onsets (i.e., the raw count divided by the number of countries in the world), and 3) the proportion of countries worldwide that had ongoing episodes. As the bar chart at the top shows, since World War II, most years have seen no more than two onsets worldwide, and these events have become even less common in the two decades since the disintegration of the Soviet Union. As the middle chart shows, those counts translate to annual incidences under 2 percent in most years, with peak rates of just 4 to 6 percent. In other words, these onsets are very rare events. In the bottom chart, we see that the global prevalence has historically been much higher, because these episodes often last for many years after they start. The share of countries with ongoing episodes of state-sponsored mass killing hovered at around 15 percent for most of the Cold War era, peaked at nearly 25 percent in the years immediately after the Cold War’s end, and then declined to recent historical lows by the start of the 2010s.

Occurrences of State-Sponsored Mass Killing Worldwide, 1945-2012

Occurrences of State-Sponsored Mass Killing Worldwide, 1945-2012

We can also look at changes over time in the geographic distribution of these episodes by mapping them. The GIF below animates a sequence of yearly maps from 1946 through 2012 that show where new episodes erupted (brown) and where ongoing ones continued (orange). You’ll need to click on the image to get it to play. I made the maps in R’s ‘worldmap‘ package and used the aptly named ‘animation‘ package to animate them. As the maps show, in the immediate aftermath of World War II, virtually all of the identified episodes of state-sponsored mass killing were occurring in Europe. Since the 1950s, though, the locus of these events has shifted, mostly to Asia, Africa, and the former Soviet Union, and a few clusters of onsets have occurred in conjunction with phases of decolonization or state dissolution.


Watch this space for more on the multimodel ensemble I’m building to forecast these onsets and the pilot early-warning program those forecasts will inform.

Update: You can now find the R script I used to produce these visualizations on Github, here. The data are on my Google Drive, here.

Leave a comment


  1. I think it’s a big mistake to look only after World War II. In my research of how collapses work (you are looking at specific collapses), societies follow the same collapse patterns as forests. The future is heavily influenced by a positive feedback loop of history. The suppression of collapses leads to a massive unstoppable collapse – the Depression plus World War II, or the massive forest fire.

    Since your research starts at the very beginning of a new relatively stable period (the period after a massive forest fire), you do not know what happens right when the world starts to become unstable – the period leading up to and including the Great Depression and World War II.

    With the financial crisis of 2008, we have entered a new unstable period – ‘the new abnormal.’ If something big is going to happen, then it is going to happen within the next 10 to 15 years. What happened during this same period right before the Great Depression and World War II?

    • Very interesting idea, thank you. The main thing preventing me from taking a longer look as you suggest is the lack of data. Even if we could construct a longer event history of mass-killing episodes, I think we’d have a very hard time assembling data on potential predictors before World War II. If you think I’m wrong about that, though, please let me know and point me in the right direction.

  2. Oral Hazard

     /  August 2, 2013

    Indonesia 1965-66, just two years. But some 2.5 million dead.

    • Yes. And Rwanda’s so small and short that it’s hard to see at all.

      In a future iteration, I might try to incorporate information about the scale of killing into the maps, perhaps with shades of orange or something.

      Of course, the deeper point here is that the very exercise of producing maps like these on a topic like this is, at some level, absurd.

  3. kucing

     /  August 10, 2013

    Yes you are so incorrect about Indonesia. It only happens shortly as US sponsored the communist cleaning in Indonesia. It doest even last for decades as you showed there

    • Actually, the data only show the anti-Communist mass killing spanning 1965 and 1966 as you indicate, but they also show a few other episodes of mass killing in Indonesia since then: one in West Papua starting in 1969, another in East Timor starting in 1975, and then another in Aceh starting in 1989.

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