OK, so maybe this is just a temporary breather after the bloodbath that was the previous century? Nope -- it's part of a long-term trend. As crazy as it seems to suggest it, the past couple of hundred years have been the most peaceful in world history. That's including the world wars.
(The numbers don't lie: Property crime, theft, and burglary have also all been dropping since around 1993. The De-Textbook has more on why you'd be just as safe leaving your doors unlocked now as your grandparents were in "the good old days.")
Yes, in absolute numbers, more people died violently in the 20th century than in any other century -- but that's because there are so many more people now. The chances that a person living in the 20th century would die violently were about 3 percent. That's a historically low number -- it was five times higher in prehistoric societies. In tribal societies, war was a daily occurrence -- just the process of everyone settling down into large-scale governments, even violent ones, was an improvement. If our hunter-gatherer ancestors could see us now, they'd be confounded by the complete lack of annual head smashing and face stabbing (if you ever unfreeze a caveman, show him our violent video games -- he'll go nuts for that shit).
Especially when you show him how to teabag.
And it's not just war, it's all violent deaths -- in 14th century England, some cities had a homicide rate as high as 110 per 100,000 citizens. London's homicide rate in 2012 was just under 1 per 100,000. And we've previously talked about how violent crime is dropping to historic lows, even in the gun-crazy USA. No matter how you break it down, violence is slowly going out of style.