Why Violence Has Declined
* Book: Steve Pinker. The Better Angels of Our Nature: Why Violence Has Declined.
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"Reviewing it for the New York Times Book Review, the philosopher Peter Singer called it “a supremely important book". 
Full interview by Sam Harris at http://www.samharris.org/blog/item/qa-with-steven-pinker/
"I suspect that when most people hear the thesis of your book—that human violence has steadily declined—they are skeptical: Wasn’t the 20th century the most violent in history?
Probably not. Data from previous centuries are far less complete, but the existing estimates of death tolls, when calculated as a proportion of the world’s population at the time, show at least nine atrocities before the 20th century (that we know of) which may have been worse than World War II. They arose from collapsing empires, horse tribe invasions, the slave trade, and the annihilation of native peoples, with wars of religion close behind. World War I doesn’t even make the top ten.
Also, a century comprises a hundred years, not just fifty, and the second half of the 20th century was host to a Long Peace among great powers and developed nations (the subject of one of the book’s chapters) and more recently, to a New Peace in the rest of the world (the subject of another chapter), with unusually low rates of warfare." (http://integral-options.blogspot.com/2011/10/steven-pinkers-better-angels-of-our.html)