So two races are debating going to war over... what exactly? You say they were clashing over the rights to the prisoners, and those prisoners were considered "lesser" races. Wouldn't the prisoners be under the jurisdiction of whoever captured them? There doesn't seem to be anything the "superior" races need to clash over.
But then at the end you also ask what are the races fighting over. What? Didn't you say
Alesander wrote:
...a recent feud within two of the groups races , grew to an all out battle clashing over the rights to the prisoners in the fortress...
This feels very confusing and contradictory. Here's some advice though:
1. Giants have captured humanoids smaller than themselves. They've placed them in a mountain fortress, currently under the control of Frost Giants, however there are Hill Giant steadings in the foothills of the mountains. The Hill Giants had been intending to use the humanoids as a food source and fear starving through the winter, but the Frost Giants seek to perform cruel experiments on the humanoids to further their own scholarly pursuits. Now the barbaric simpleton hill giants have begun sieging the outer bulwarks of the frost giant fortress, giving the PCs a chance to escape
2. The PCs are goblins or other Small sized monstrous races. They've been captured by a bunch of religious zealots, preferably human but could also be dwarves, who are trying to "rehabilitate" these monstrous types. The other race, who are hobgoblins, need their slave workforce back to continue their ongoing campaigns against the theocracy.
3. PCs are some kind of fey or plant race. Currently they've been captured and held by the Evil Queen (use whatever big bad fey you'd like) and are being watched by mites, pechs and korred loyal to her. The rival faction is led by the queen's sister (use another powerful CN fey) and she has her kingdom in the forests dotting the lower peaks. The hapless mortals all through the mountain areas are being caught in a shadow war born of the First World that has spilled over into the Prime
Also, if the 2 "superior" races aren't, in fact, warring over their prisoners, you could use the following motivations:
1. Control over the mountains and all of their resources
2. Above ground versus below ground superiority
3. Some personal slight (real or perceived) from one "superior" race to another
That last one is a good one for the fey queens. You could have it be some family squabble, like mom always loved you best or one sister stole the other's consort or something, and the mortals are just caught in the crossfire.
