Another realist explanation of international politics, John J. Mearsheimer's The Tragedy of Great Power Politics provided a slightly different take than Waltz or James had. He argues for a more aggresive version which he terms offensive realism. The main difference most likely being that in his system, states seek hegemonic power and not just a balance of powers in order to ensure their continued survival.
I did not admittedly, if shamefully, read the whole book, as I have started to realize that I should probably start working on my master thesis in a little more goal-orientated form. Yet, I found Mearsheimer's comments and analysis interesting even if at times more like a blueprint against which I can argue. As an introduction to realist thought I would definitely recommend this over either Waltz or James simply because it is a lot easier to read and understand. Don't stop with him though, Waltz is a lot more encompassing and in the end makes a more persuavive argument in my opinion.