A later important follow-up was The Better Angels of Our Nature - Why Violence Has Declined. The central argument of this book is that everyone whining about how things are going downhill in society and the world is going to Hell in a handbasket is, quite simply, wrong. Oh.... and here's 700 pages of the evidence why they're wrong. Which would seem to qualify this as one of the most important non-fiction books ever written.
He recently gave the talk below, which seems to be a bridge between his last book, Angels, and his forthcoming book, Enlightenment Now, which seems to be about how the values of the enlightenment are the best way forward if we want to continue the trends highlighted before.