“One always tends to overpraise a long book because one has got through it.” — E.M. Forster (Attributable of course to cognitive dissonance.)
In that spirit Steven Pinker's On the Better Angels of our Nature is brilliant. It's the book of the century!
It's on "the decline of violence in history and its causes". The Preface sets out the argument very succinctly, so you don't really have to read the rest. The main body smacks of protesting too much, but I'm not a historian and really capable of evaluating the evidence Pinker cites; but then, nor is he. Other critics have complained about his use of relative rates of violence (instances per 100,000 population raather than absolute figures) as if it were a sleight of hand. I can't, for example, comment knowledgeably on that. I am largely convinced by what Pinker discusses, but then I don't know enough to know what he doesn't discuss, and the counter-arguments and counter-evidence.
The final chapter on game theory and violence is more convincing. But overall, I'm not convinced that Pinker has added very much to Robert Wright's argument in Nonzero: History, Evolution & Human Cooperation: The Logic of Human Destiny (2001)--certainly not 700 pages worth.