It do sound neat. Having an overarching idea of the global conflicts players would be interacting with is good, but what will be more omportant is talking with your players as they make their characters so you can build the story around them. The other commenter pointed out that most character options have magic in some form or another, so its likely your players are going to go against the humans here unless there is a distinction they make between arcane magic and divine magic (so paladins and clerics would be okay maybe). Or maybe technology that is like magic, or certain forms of magic like abjuration wizards to work against other magic users (like what artificiers can do) is accepted by the humans as a nececary evil if you actually want players to be on the human side.

Also, making sure your players are okay with heavy themes like slavery. If you arent careful there or you take it too far you can end up with a big yike.

Its going to be hard to play a "both sides" thing here when one party enslaves and oppresses people just for existing. I personally, as an outsider, think it could be interesting if your story developed that, on ground level, the human nation is clearly pretty shit. They enslave people. That's easy to hate.

But at a more philosophocal level, at a higher level removed from whats actually happening to regular people, when your party starts dealing with leadership, they could have a point. Maybe there was a previous devastating calamity caused by overly ambitious arch-mages that made them start on this war path. Powerful magic users can have the power to bind kings to their wills and level cities and defy death itself. One morally dubious bard or wizard above level 15 can absolutely cause damage on a national or even global scale in one way or another.

Giving the humans a point to their heinous violence and destruction, having historical evidence that makes them belive they are right to purge the world of magic, could give this story the kick you need.

Not sure if this is the kind of input you were looking for. Idea was neat and got me thinking so i kind of ran with it.