The Better Angels of Our Nature: Why Violence Has Declined

Although it took me a long time to read, (this is a very dense book, well written but full of examples of statistics) I would recommend it to anyone and everyone.
Steven Pinker proves that our world is getting less violent. This is flatly contradicted by our senses and experience every day. Any person alive now will be inundated with news of terrible violence around the world and believe that it's getting worse.
All the proof is here. Examined from all sorts of angles, with doubts and attempts to disprove thrown in, as in all good science. But the proof still stands.
It doesn't shy away from reality and includes all the atrocities and massacres but puts them into a greater context of all of humanity's history.
This is one book that truly has changed my life, and it continues to protect me from tendencies to total cynicism and pessimism.