Unfortunately, I have never read Guns of August; although I have heard it is a classic. It appears that you are interested in World War I. I would like to make a recommendation to you. Dreadnought: Britain, Germany and the Coming of the Great War by Robert K. Massie is an outstanding book. Have you ever wondered how Great Britain went from a close relationship with Prussia (later Germany) to an alliance with their historical nemesis France? In this book Massie traces how that happened and why it happened. Makes fascinating reading of an event that,in many respects, set the stage for the 20th century. If you haven’t read it hope you enjoy it.

I would recommend A World Undone by G J Meyer. I personally find it to be one of the best single volume histories of World War 1, and the way he does an insert of background information as he tells the history never feels like its interrupting and was a great way to get a clearer picture of what was going on. For instance, he is talking about the Balkans, and Serbia in particular. He inserts a quick bit of background with a brief history of Serbia at that point. And it's not a footnote either, it's a couple of pages, and then back to what he was originally talking about.