The decline of war as a cause of human mortality

With recent events in Iraq, Syria, Gaza and parts of Africa, and shortly after the century in which millions were killed Stalin, Hitler, and Mao, Steven Pinker’s claim that the human impact of war and conflict has been diminishing may seem crazy. His book “The Better Angels of our Nature: why violence has declined” assembles data from a large number of sources and studies and points convincingly to exactly that conclusion.

“To be sure, any attempt to document changes in violence must be soaked in uncertainty. In much of the world, the distant past was a tree falling in the forest with no one to hear it, and, even for events in the historical record, statistics are spotty until recent periods. Long-term trends can be discerned only by smoothing out zigzags and spikes of horrific bloodletting. And the choice to focus on relative rather than absolute numbers brings up the moral imponderable of whether it is worse for 50 percent of a population of 100 to be killed or 1 percent in a population of one billion.”
“Yet, despite these caveats, a picture is taking shape. The decline of violence is a fractal phenomenon, visible at the scale of millennia, centuries, decades, and years. It applies over several orders of magnitude of violence, from genocide to war to rioting to homicide to the treatment of children and animals. And it appears to be a worldwide trend, though not a homogeneous one. The leading edge has been in Western societies, especially England and Holland, and there seems to have been a tipping point at the onset of the Age of Reason in the early seventeenth century.”
Stephen Pinker on the Decline of War. Source:

Pinker assembles archaeological, anthropological and historical data and guesstimes that suggest that pre-state societies were far more violent than our own (see following figure). If the wars of the twentieth century had killed the same proportion of the population that die in the wars of a typical tribal society, there would have been two billion deaths, not 100 million. Historical estimates of conflict death rates are hard to find, but suggest that the intensity of conflicts and the population-level death rates were often higher than in recent decades. He quotes the Human Security Brief 2006, which estimates that the number of battle deaths in interstate wars has declined from more than 65,000 per year in the 1950s to less than 2,000 per year in this decade – but more on this below.

In Western Europe and the Americas, the second half of the century saw a steep decline in the number of wars, military coups, and deadly ethnic riots. After the cold war, every part of the world saw a steep drop-off in state-based conflicts, and those that do occur are more likely to end in negotiated settlements rather than being fought to the bitter end. Political scientist Barbara Harff has also estimated that between 1989 and 2005 the number of campaigns of mass killing of civilians decreased by 90 percent.

As part of my team’s update of estimates of global, regional and country-level deaths by cause for years 2000-2012, released on the WHO website earlier this year (, I updated the WHO estimates of conflict deaths. Methods used previously by WHO for estimation of direct conflict deaths were developed in the early 2000s and applied adjustment factors for under-reporting to estimates of battlefield or conflict deaths from a variety of published and unpublished conflict mortality databases.

The revised WHO country-specific estimates of war and conflict deaths for the period 1990-2011 make use of estimates of direct deaths from three datasets: Battle-Related Deaths (version 5), Non-State Conflict Dataset (UCDP version 2.4), and One-sided Violence Dataset (UCDP version 1.4) from 1989 to 2011 (International Peace Research Institute 2012. UCDP/PRIO datasets). Using these three datasets, instead of focusing solely on battle-related deaths, reduces the likelihood that overall direct conflict deaths are underestimated. However, it likely that a degree of undercounting still occurs in the count-based datasets, and a revised adjustment factor is applied to the annual battle death main estimates for state-state conflicts. No adjustments were applied to estimated conflict deaths (main estimates) for non-state conflict deaths, and one-sided violence. Additional information from epidemiological studies, surveys and other sources were also used for Iraq and Syria. Methods are documented in more detail in the Global Health Estimates Technical Paper 3 (2013):  “WHO methods and data sources for global causes of death 2000-2011”

The following figure compares these updated WHO estimates for years 1990,1995, 2000, 2005 and 2010, with the simple sum of the deaths in the three UCDC-PRIO datasets, and also with the conflict deaths estimated by the IHME Global Burden of Disease 2010 study (published in the Lancet in December 2012). While conflict deaths for individual years vary considerably, there is some evidence of a general downward trend, with an estimated 57,000 deaths in 2010 compared to 138,000 in 1990. Unfortunately, the conflict in Syria has resulted in an increase in conflict deaths in 2011-2013. These estimates are considerably lower than earlier WHO estimates, and also than those made by the original Global Burden of Disease Study published in 1996. That study estimates a total of 502,000 conflict deaths in 1990 and projected that it would be 834,000 in 2010.

As can be seen in the Figure, the GBD 2010 estimates for conflict deaths are considerable lower than the revised WHO estimates, but also for three of the years shown above, lower than the main estimates from the UCDC-PRIO databases.

        War and conflict deaths per year: comparison of three sets of estimatesWHO conflict deaths
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