Please take a look at: What are the chances of a third world war?
I think Pinker is a great writer and enjoy his work. However, I need to retract my endorsement from four years ago of his claim -- namely, that we are living in the most peaceful period of human history and society as a whole is becoming less violent. Taleb's work on black swans / fat tails clearly argues that Pinker isn't being rigorous in his statistics, since he uses stats in a thin-tail mechanistic way, a way in appropriate for analyzing something like the history of violence (for in-depth technical consideration see Silent Risk).
From the first link above, Pinker is making the same "fooled by randomness" argument that H.T. Buckle made in 1860:
That this barbarous pursuit is, in the progress of society, steadily declining, must be evident, even to the most hasty reader of European history. If we compare one country with another, we shall find that for a very long period wars have been becoming less frequent; and now so clearly is the movement marked, that, until the late commencement of hostilities, we had remained at peace for nearly forty years: a circumstance unparalleled (...) The question arises, as to what share our moral feelings have had in bringing about this great improvement.