I've read two disappointing books recently, so in the interest of helping others avoid the mistake, I'll share.
"Castles, Battles, and Bombs" by Jurgen Brauer and Hubert van Tuyll has a very clear concept: the authors attempt to study military history through the tools of standard (aka neoclassical) economics. They choose six periods of history, pair them with six principles of economics (opportunity cost, substitution effects, marginal cost vs. marginal beenfit, etc.) and attempt to use the economics principle to understand the period of history.
It's a neat idea; too bad it doesn't add much to the understanding of history. Now, I'm not saying the authors are wrong in their observations. Yes, clearly, building castles in the High Middle Ages reduced the funds kings had available to devote to maintaining field armies. But what was true in pretty much every one of the six chapter of this book is that the economic principle, while at least somewhat applicable, is not key to understanding the period in question.
For instance, they study Renaissance Italy via the economic question known as the principal-agent problem, which is to say, when you hire something to do something, how do you know they (your agent) are doing what you (the principal) want? Since Italy was constantly at war through most of this period, and that war was primarily conducted via hired mercenaries, the condottori (literally meaning contractors), it's easy to see why they matched the two.
While the book goes through the considerable lengths the Italian city-states went to in order to mitigate the principal-agent problem, all of which make sense (essentially, an auditing corps of city employees were used to keep track of the activities of the condottieri, as well as a tendancy for longer-term relationships), it's not believable that the principal-agent problem was a cause for the commencement or ending of this era. The principal-agent problem has to be managed any time you engage in a contract, yes; but since the problem existed throughout the era in study, and roughly equally for all participants, I felt like I learned nothing new about the era by studying these. The real reasons why the mercenary system existed during that era, why the city-states chose it, and why they eventually chose otherwise, all lie outside the area of study.
Every chapter suffers from this failing, in that while the principle does apply, it doesn't offer key insights. In the fifth chapter of the book, they go over the well-trodden data showing that (non-nuclear) strategic bombing is not economically justifiable. That is to say, the total economic costs to an aggressor country of building and operating a combined-arms air force capable of conducting a strategic bombing campaign is greater than the economic damage done to the enemy by said campaign (factories, surprisingly, turn out to be pretty easy to repair). They use the extensive data on WWII's air campaign against Germany to show this. Unfortunately, as they acknowledge, even the post-war analysis within the US military reached the same conclusion about cost-benfits 60 years ago. They claim this is a lesson in marginal cost vs. marginal benefit, but in fact what the data show is that it's simply a bad military investment in the first place, you don't have to think about marginal cost vs. marginal benefit. Allocating those resources to tactical air support of operations instead of conducting strategic bombing at all is the conclusion supported by the data.
The worst case of this is the chapter on castle-building vs. field army maintenance in the High Middle Ages. They attempt to pitch the preference for castle-building as causing a lost opportunity, in that the monarchs couldn't also maintain a field army. But what their data shows is that the cost of castle-building, even for aggressive castle builders like Edward I in England, pales beside the costs of war. Their own data shows Edward spent £90,000 on Welsh castles, but £1,400,000 on fielding armies for his wars against Wales, Scotland, and France. Castles are so cheap relative to armies that it's distorting the data to say they represented a lost opportunity.
In the end, this book does explore its thesis. Unfortunately, I think the book shows that the thesis isn't worth taking much farther. Is it helpful for a historian to understand the basic principles of economics? Yes. But will they be a primary guide to understanding past actions? Based on these examples, no.