Mainly some short-comments on the book. The kingdom faces an invasion from some primeval beings. I don’t know if I would compare them to elves. I think they are some kind of dark Norse elf. The invaders aren’t good, obviously, but they aren’t evil in intention.
The kingdom has to rally support from its southern neighbors. On the other hand, the southernmost kingdom is preparing to invade the Northern kingdom (obviously, this is a reference to the Ottoman empire).
There are main characters interspersed throughout the locales and their lives are slowly woven together.
As far as fantasy novels go, this is series is pretty good. Williams is a talented writer, as evident in his other series (even if he makes some major goofs). I think the setting here is late middle ages, since one empire is referenced as having gunpowder.