Although this series is mostly about the structure of military units and this is about trying to piece together the structure of the Roman Army of the Republic during this critical period it also provides a really good (and mercifully quick) history of the Punic Wars in the process.
Fields starts with the Roman expansion and absorption of the Latins, and the rest of Italy to set us up for the conflict.
There is almost nothing in here about the final Punic War and destruction of Carthage really so don't expect much about the period after Zama except for the brief mentions regarding that last war being prosecuted by Scipio Aemilianus who was the grandson of a consul who died at Cannae and the adopted son of Scipio Africanus and who was the sponsor of one of our chief sources for this period--Polybius. This is important because it prepares us for understanding the potential biases in Polybius.
Even though this is a book about the Roman Army, it is as much about (naturally) the Carthaginians--really the Barcids, we should say. Hamilcar, Hannibal and the rest come out of this book with some seriously burnished reputations. Fields makes a strong case for Hannibal both as a tactician and as a strategist. Ultimately Fields says that Hannibal did the logical things that he should have done given his war aims and resources. He also reinterprets the famous oath that Hannibal took to never be a "friend of Rome" which he contextualizes as being a declaration of the strategic goal of reversing the subservience of Carthage in the Western Mediterranean after the first war since "friend of Rome" was a very specific euphemism for "vassal."
Fields proposes that Hannibal's aim wasn't the total destruction of Rome (thus answering the "why didn't he just march on Rome" question that plagues a lot of people) but instead was the idea of destroying Rome's power by detaching the Italian allies (through a demonstration of superior power by defeating army after army).
What Hannibal couldn't really know going into it (and our lesson from it) was that A) Rome had a lot of manpower (a point made clear here since the whole point of the book is to demonstrate the structure of the Roman Army and how it was organized) and B) how fully integrated into the Roman world many of the allies were. True, there were defections, but it's worth noting that one of the real revelatory things for me from this book was that when we talk about a Roman "consular army" of this period it consisted of 2 legions of Roman troops and basically the same number of allied infantry plus allied cavalry that were in greater numbers than the Roman cavalry contingent.
Even more critical here is that the allied cavalry were basically equipped and organized in the same way as the Roman infantry so even though on paper we don't call their units legions and maintain this distinction on the ground they were basically the same and were also led by Roman officers.
This integration is itself one of the reasons why the allies did eventually agitate for more rights because by the time of the Social War they had long since been the same as Romans on the ground where it mattered--on the battlefield, bleeding next to Romans.
A couple of other points here. While Hannibal gets his reputation restored (and Hamilcar too) -- we also get an interesting insight into the fact that the core of Scipio's successful army consisted of the survivors of the early defeats who had been penalized by their fellow citizens and sent away to serve out their penance for losing but who brought with them the most experience dealing with Hannibal--even if that experience was one of defeat.
So, for a book that could have just been conceived of as a glorified set of org charts Fields delivers a lot more things to chew on.
Happily, Fields also authored similar volumes on the Roman Army of the Civil Wars and of the Principate which I'm looking forward to moving on to after this one.