Return of the Danu by Kelly Lucille

Prince Ansgar The Bloody has no love for magic users, and he trusts the Danu even less than the magic shrouded Green they command.
Elena has spent her whole life hiding from the Warriors of the South after they burned her beloved Green and killed most of her people in their bid to take the North Lands, she is not about to start trusting them now. Certainly not the heir apparent, and the man they call ‘The Bloody’.
Both have good reason to hate, yet somehow the fate of the known world is suddenly thrust on their unlikely shoulders. They will have to find a way to work together or everyone will suffer, because the burning of the Green caused side effects none of them could have foreseen. A new alliance between the Danu and the southern conquerors may be all that keeps the people of the North Lands safe from a wild that has grown it’s own magic teeth.
…And not everyone wants to see the peace accords succeed.