When a fabulous resource takes its place in my hands, I must write about it. Even though it is not directly related to fantasy or science fiction, this book may improve your combat scenes or even inspire a whole story, the way it did for me a month ago. I was reading a passage about Roland and Charlemagne and got an idea for the mythological creature story I wanted to write for a contest. I didn't finish the story in time, but I still like the idea enough that I will finish it anyway.
By the Sword: A History of Gladiators, Musketeers, Samurai, Swashbucklers, and Olympic Champions by Richard Cohen has a wealth of material that is more readable than you might expect from a history book. His prologue invites you to join him in learning more about his passion, beginning with a quote from Dune about the beginning being the time to make sure the balances are correct.
I would say that he does well in balancing the facts with a style that people can relate to. His anecdote about his first and only duel thirty years prior to writing the book drew me in. His facts are clearly written in an entertaining style. Now don't think that sword fighting is all honor and glory or even Hollywood glamor; it's bloody sport, even when blood isn't literally involved. Honor sometimes goes out the window when ambition is involved. Cohen covers the good, the bad, the noble, and the ugly in his historical account. As he says at the end of the prologue, "Above all, I have tried to portray the character of swordplay--at once graceful and brutish, fiercely competitive and technically beautiful, life-threatening and life-enhancing."
Even if you don't need By the Sword for your writing, it is still far more interesting than the typical history book. It will give you a greater understanding of several periods of history and of sword fighting itself.