As a student of koryu bujutsu, I have a shelf full of martial arts books, both technical and philosophical. Karl Friday's Legacies of the Swords is one of my reference works. Friday is both an academic and a student of bugei and as such well-qualified to write in-depth about the Japanese warrior tradition and Samurai martial culture.
A well-written treatise that is required readers for serious martial artists and students of koryu bujutsu.