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Grammar correction
John Doucette
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Did some more research on this tonight, and was able to answer my own question, at least to some extent.

The conclusions seem to be:

  1. For the world as a whole, this is a very unlikely claim.
  2. For the country of America in particular, this likely true, at least for the deaths of Americans in wars since the country was founded. This is possibly the origin of the claim, at least in my region, which I`ve often seen made by Americans (i.e. More Americans have been killed by cars than by all wars combined becomes More People have been killed by cars than by all wars combined.) The claim is also likely to be true in many other individual countries.
  3. For this claim to become true for the world in general in the future, the bulk of the world's population would have to be at peace for a very long time, and average car safety would have to decline.

Evidence against the worldwide claim:

  1. This similar question has an answer which puts a lower bound on the number of humans killed in war in the 20th century at an estimate 200 million.

  2. A reference cited by this quite interesting WHO report (page 33), puts the cumulative total number of deaths by automobile at 25 million, conservatively, in 1997. Unfortunately I can't get access to the reference directly to see what methodology was used.

  3. A recent WHO report estimates the number of fatalities due to automobiles in 2013 at 1.2 million (worldwide).

  4. If we made a very generous estimate based on 2 and 3, doubling the conservative estimate of 25 million by 1997 to 50 million, and assume that 2 million a year were killed 1997-2014, rather than the fewer than 1.2 million that seems probable, we still get less than 90 million total deaths due to automobiles. This is less than the number of people killed in all wars, worldwide, in the 20th century alone, and in fact, is less than half the number required.

Evidence for the claim being true in America:

  1. Assume that the original claim was more people have been killed by cars than by warfare, in the history of the country of the United States of America.

  2. This table on Wikipedia (which seems to be sourced from the US government's NHTSA FARS database) gives a list of recorded US traffic fatalities going back to 1899. The total number of deaths is 3,581,306 (my computation via a spreadsheet).

  3. This table on Wikipedia gives the total number of American military deaths as 1,321,612, though the estimates come from a lot of different sources. Major deployments that were not "proper" wars are also included.

  4. The only major conflict in which US civilians died in large numbers (to my knowledge) is the US civil war. There is considerable debate on how many civilians died in total, and no official records were kept at the time. Wikipedia (4th paragraph) suggests the number is unknown, though it cites a poor source. However, I cannot find anything better than wild speculation on enthusiast websites beyond this. The highest estimate I see anywhere is around 800,000 dead, mostly slaves. This would have been nearly 25% of the enslaved population, and about equal to the total number of soldiers that died. and seems an overly high estimate. If anyone has better data, I'd really like to see it!

  5. In recent wars in Iraq and Afghanistan, US contractors have been killed in fairly substantial numbers. However, Reuters puts the total number of contractors killed in Iraq by 2007, who were also US citizens, at just 224. I cannot find a similar number for Afghanistan, but this at least gives us a ballpark.

  6. In total then, I estimate the number of American civilians and military personal who have died as a direct result of warfare at no more than about 2.5 million. This is less than the total number of Americans killed in motor vehicle accidents, for which we have very good data.

Evidence that the worldwide claim is unlikely to be true in future:

  1. At current rates, we'd need a century of world peace for cars to catch up to the 20th century death toll alone. This seems very unlikely.

  2. The current tread is for car safety to improve over time. With inventions like self-driving cars, this tread may even accelerate. Therefore, it is likely that more than a century or world peace is needed.

Final note:

  1. It is quite likely that in other countries that have not seen large scale total wars fought on their soil, the claim is true as well. Most of the 20th century death toll is concentrated in specific countries, especially Russia, China, and Germany. Countries that remained neutral during major conflicts like Holland, Sweden, or Switzerland, are probable candidates.
John Doucette
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