If Jack is either a warrior or a wizard he'll be forced to slaughter the other side too, because they would rather let the world end than work with you.
Horvath and his wizards decided non-magic-users were sub-human, and as a warrior their shops won't serve you and you get arrested on trumped up charges as soon as you enter their city. Horrendous and his warriors decided that Magic is Evil and arrest wizards on sight as a wizard you discover these people are taken to a secret underground prison and tortured to death. Without necromancers to hate the warriors and wizards turned on each other. Black-and-Grey Morality: Hecubah and her necromancers are totally evil and want to kill or enslave ( or kill AND enslave) everyone else in the world, but it's not like the rest of the world is much better.
Anti-Grinding: Weaker enemies stop giving XP if you're too far above them in power.Hecubah, having somehow been "purified" of her Necromancer traits, no longer has any memory of who she is, and it's strongly implied Jack is going to make her his girlfriend now. Amnesiac Lover: Heavily implied in the wizards' ending.