Though violence has indisputably declined, Dr. Pinker says, it could rise again. But by understanding the causes of the decline, humanity can work to promote peace. He endorses the new book “Winning the War on War” (Dutton/Penguin), by the political scientist Joshua S. Goldstein, which argues that the slogan “If you want peace, fight for justice” is precisely the wrong advice.
If you want peace, Dr. Goldstein argues, work for peace. Dr. Pinker agrees.
...If you want peace, understand psychology.