It's a fantasy in that it's about a world that's not ours, a pre/early modern world including some fantasy tropes and feudal vassal states, etc. I've heard it called "hard fantasy," which makes some sense given how well constructed and thought out the setting is. You will not find dragons and magic; though magic is talked about, it's talked about somewhat like the real world: as superstition.

Great book. Looking forward to the fourth book coming out before reading the whole series.