Armstrong makes a compelling case, even when she discusses the Middle Ages when the Holy Roman Empire held sway over Europe and the Crusaders went to Jerusalem to take back the Holy Land. Even the so-called Religious Wars weren't drawn along the lines of religion, and adherents of different beliefs fought on the same sides. And when it comes to more modern times she explains how religion became the more personal belief we have today and how nationalism became the driving force for violence with the rise of nation states.
Not only is this book very well-researched, it is also very methodical and almost painstaking in its delivery and does so in a very scholarly and academic manner. I felt I was in over my head until it got to more modern times and although I sometimes felt like abandoning the book early on, I'm glad I kept at it. In fact, there's so much information here I feel like this is a book I'd like to re-read again in a few years. I didn’t always find it thoroughly convincing, although that might be due to my unfamiliarity with much of the history, but sometimes it felt like Armstrong was squirming a bit to explain some more modern troubles. But it's a solid and thought-provoking counter-argument to books that claim any gains in peace are due solely to "Enlightenment philosophies" (which she ties to the rise of nation-states and nationalism) and I’m sure I'm doing a poor job of explaining her arguments. But personally, my greatest qualm with the book – as a religious person – is that it’s written with such an agnostic viewpoint that it felt like it was defending the benefits of religious belief systems while denying the Godly power behind them, but I understand the need for a scholarly viewpoint. (I received this book from the BloggingforBooks program in exchange for an unbiased review.)