Are the Caradysh even evil? Urth certainly is the kind of ruthless, monologuing bastard we don't want to see ascend to divinity, but the civilization as a whole don't seem as bad save for their leadership, though granted, we don't see much of them outside the daughters who are undoubtedly indoctrinated from birth.
As for the whole undead thing, I'd argue that isn't inherently evil, though I can't argue that most people, especially in these early ages, wouldn't ever consider an alternative to undead horde = ultimate evil.
Granted, it is completely beyond our ability to see Urth permakilled and make a more lasting peace with the less comically villainous portion of their civ, I wouldn't even know where to begin.
War clearly hasn't worked out for us, so I'm for for forging ties against the southerners (common enemy) such that the northern civs are reluctant to war amongst themselves.
Hopefully, with focus on diplomacy we can influence the lowlanders and his rogue daughter to lean our way instead of his.
P.S. Clarifying: Urth literally got caught monologuing in a fashion that Syndrome would sigh at, thus letting his prisoner effect their final sacrifice. That's about as supervillian as it gets.