Humans is an obvious choice. But it's not just that simple. The kingdoms have many races that support the kingdom's cause. Example that I came up with earlier: 

Human kingdom (Working on a name -> mostly pure races):
- humans
- elves (whatever varieties)
- fairies
Etc.

Orc kingdom (-/-)
- orcs
- werewolves
- minotaurs
- ogres
Etc.

I don't want it to sound too WoW-ish tho.
This is just an example to give you the idea of what I mean with the word kingdom. Each a home to different species. We can also add neutrals of course. -> enemies to both.

- undead
- dragons/dangerous wildlife

You can expand on the races as well.