I've recently finished reading Thucydides' classic History of the Peloponnesian War. It was not an easy read, and I would not recommend it to the layperson. There are other, easier texts to read when starting out in the history genre and military history genre specifically. Thucydides' style can be difficult to follow. In his criticism of his predecessors such as Herodotus, Thucydides sought to embark on a different path for his own History - one that was explicitly factual, free from speculation and poetic license as much as possible. While from the standpoint of veracity this is commendable, Thucydides' strictly factual approach can often be exhausting to the reader. At times, his History reads like a Linear B tablet from Greece's Bronze Age, an exhaustive list of places and things (somewhat like the Catalog of Ships in Book 2 of Homer's Iliad, a poem that Thucydides criticized on historical grounds).
However, despite these exhaustive lists, the heart of Thucydides' History is excellent and well worth reading. His exploration of human behavior in the face of power, man as a political animal, the nature of international relations, war's impact on the civilizations and states that fight them, and the frailty of civilized regimes in general, is timeless. The conflicts between the Athenian Empire and Sparta and its allies, and more importantly, the way people at the time responded to those conflicts, could easily have been transplanted to any other time or place.
One chapter that was particularly compelling to me was when Thucydides described the civil war in Corcyra. Corcyra, it will be noted, was one of the reasons why the Peloponnesian War itself was instigated. Now, civil unrest occurred between the pro-Athenian faction and the pro-Spartan faction in the city. The civil unrest led to poison partisanship and a power vacuum, in which cruelties abounded. Civilization quickly fell away, the restraining mask removed. Unfortunately, the relevant passages are too long to be quoted here, but they can be found in the "Civil War in Corcyra" chapter in Book 3.
Another compelling part of Thucydides' History was his recount of the disastrous Sicilian Expedition, which permanently crippled Athenian power. It is at once a magnificent tale of a city's optimistic celebration of its resources (he is quite detailed about the amount of troops and ships gathered at the harbor of Piraeus as a grand display before the start of the expedition) at the peak of its power, the warnings against overreach and demagoguery in the case of Alcibiades, the struggle of a people against those that would conquer them, and the disastrous results of hubris.
The military exploits themselves ranged from hard to read lists as described above, to vivid details of campaign, maneuver, and battle, as at the Sicilian Expedition. In his description of the Siege of Syracuse, it is quite obvious that Edward Creasy's primary source is Thucydides.
While much of the book was tedious, and some chapters, such as the chapter on Persian intervention after Athens' defeat in Sicily, are too long and stray beyond the main topic discussed, Thucydides' History is an invaluable insight into human nature and political organization, and the foundation of political realism. I would not recommend it to the layperson, but if you have some experience under your belt in this genre, it is definitely well worth your time. The version I read was the Penguin Classics version (affiliate link), which flowed very well, but you can easily find other translations for free on the internet.
The next book to be reviewed is Thomas Sowell's The Vision of the Anointed.