May I suggest a couple of books to you? The first is The Complete Roman Army by Adrian Goldswothy, Amazon price: $13.58
This is a fantastic book. It presents the Roman Army in a light that I have never before seen. Among other things, it presents the Romans as a people who fought their wars "to the knife" or to the destruction or absolute subjugation of their opponents. This was in a world of the Successor Kingdoms to Alexander where the various kings would send their professional mercenary armies out to fight set-piece battles and then retire to negotiate terms for the winners. This does explain much about why Hannibal never actually cut Rome down when he had the chance after Cannae. It was not in his culture to do so, he was waiting for Rome to come to the negotiating table like a civilized state. Good luck!! He got Publius Cornelius Scipio invading Africa and the head his brother, Hasdrubal, tossed into his camp instead. There are other equally good books by Goldsworthy.
Another is Rubicon: The Last Years of the Roman Republic by Tom Holland, Amazon price: $10.20. This is less a military history of the Civil Wars than a political history of the period of Roman history from the time of the Brothers Gracchi to the Battle of Actium in 31 BCE where Octavian and Agrippa beat Antony and Cleopatra, leaving Octavian to become the First Man (Princips) of Rome. Octavian may have been a sneaky bastard compared to Marcus Antonius but he was a political genius who put his great uncle, Caius Julius Caesar, in the shade for political smarts. The book charts the careers of the Gracchi, Marius, Sulla, Crassus, Pompey, Caesar, Antony, Octavian, and the assassins of Caesar. It is both political and somewhat gossipy. It is also a very good read. Holland's latest is also a very good read: Persian Fire: The First World Empire and the Battle for the West which charts the rise of the Persian Empire and the rise of Athens and Sparta and then brings them into their collision. I will tell you that Holland does not paint the Spartans nearly so prettily as the film, "300," does nor are his Persians anywhere near as dastardly. For the record, Sparta was a totalitarian state of the first water and that needs to be remembered. Yes, it was very instrumental in saving Western Civilization, but we need to not glorify them.
Trying to Walk in the Light, Hugh
1 John 1:5