well here an idea that you might like,
make both the humanoids, and the wilds neighboring Kingdoms of sorts, held together by a centuries old pact. long ago an enemy had shown up, that was a threat to both, nearly over coming them, but when they worked as one, they were able to scatter their enemy to the winds. since that day, the civilized kingdoms had sent tribute to the feral kingdoms of riches, foods and the cream of the crop in the new generation. in return the feral kingdoms busy themselves in constantly fighting threats to civilized kingdom and themselves, acting as a buffer and guardians of the humanoids. well after a century or too, life has become amazingly easy within the civilized kingdom, the kings have grown arrogant with their success. no longer remembering the dark days that had bound them to their neighbors, they toss aside the agreement, and refuse to send tribute, declaring themselves free of "oppression".
this of course doesn't go over well with the feral kingdoms, whom feel cheated of their earned prize, as they have been fighting constantly, though they are shrewd enough to seek a diplomatic answer, seeking to return things to how they were. things are further strained as a younger duke/king, openly attacks the feral kingdom's emissary. this nearly sets off a war, but thankfully the emissary is taken in by a more peaceful kingdom, and provided with proper care. this merely stalls a war, and turns the whole thing into a powder keg waiting to be lit.
I know a little vague, but this allows more to be added in, so others can add and change as they see fit.