How so? You can give the barbarians any type of real-world reason for conquest and decide whether or not diplomacy and intrigues will be successful in resolving the situation. Can they negotiate? Is there a charismatic leader driving them on? Can he be eliminated or can you corrupt his rivals to work against him? Is it possible for someone to pull some Joseph Smith style mind-control and convert all the barbarians to Mormonism and move them to Utah?
I used the word "monsters" for a reason. There are all sorts of reasons they're enemies, but "those who resist (and fail) suffer in ways too terrible to mention." - you're not really going to be upset to see them die.
That's the problem...finding a way that you feel that the barbarians losing is a -good- thing, without it being "kill 'em all, God knows they're not His own."
Would you be interested in allowing groups to solve the campaign in ways you never imagined, or are they pretty much all going to have to conform to your vision of proper action?
Depends on the solution. Personally, I'd like to have at least three possible solutions - the one I "intend", the one I'd be willing to see done, and something else.
Just because "canonically" it was solved one way doesn't mean it had to be done that way.
However, I don't intend to support diplomacy and intrigue as "how to win" nearly as fully - I'm fine with them working, but I'm not fine with them being so superior there's no reason not to do them.
How do you propose legislating this morality in a game system? If you've played with other humans at all, you know that some of them are going to ignore your morality and do the expedient thing if it's mechanically sound.
Which, frankly, is a bad thing. Whether doing the moral thing is important for any reason or not, one should not make IC decisions based on OOC calculations that have nothing to do with how the character would act.
Frankly, the thing is this.
Doing the right thing -is important to do-. Its not because doing the right thing wins the war faster or with less losses, its because your ultimate goal (as the Companions) is to (re)build civilization, justice, etc.
It may be expedient to treat using poison as perfectly valid, but being expedient would actually -hurt- having something worth fighting for.
If you make the enemies magically evil, then there's no chance the players can't live up to these ideals. Any action they take to thwart the barbarians is a moral one, as the barbarians are EVIL!
There are plenty of other challenges than "how many barbarians can you kill".
So you have several choices.
Do you do things the hard way, knowing that it is the right thing to do?
Do you do things the easy way, and hope that the good outweighs the bad?
Do you not care?
Ideally, you pick #1. Saying "But how do you encourage people to do that?"
Well, I would assume that if you actually -care- that it is the right thing to do, then that would matter somewhat.
If you're determined to play this as "what is the mechanically most efficient way to win", you're playing a lot of things, 98.75% acceptable (to borrow a number from Seuss) - but you're not playing the game as it was intended to be played and you would really be better off playing a game where tragedy and failure and hard work are not meant to be important elements.
I don't want to write a game that appeals to the "I want to win" side of gaming. I would like to write a game that makes your victory mean something.
And that is ultimately the thing. Yes, you can be a "pragmatic" individual using whatever means are easiest. That won't produce the best long term outcome.
If you don't care that it meant that peasants will suffer and so on, then me saying you get a lower "score" wouldn't really change that.
If you want to play someone trying to do the right thing because the right thing matters, you will see the game work as is intended to work (as in, as distinct from unintended stuff, which is not necessarily worse, just not an intended consequence).
So what path you take is up to you, within reason (horse archery doesn't -exist- here, though it may exist elsewhere in the broader setting, that broader setting is relevant to nothing in this regard).
A game that has to mechanically bribe people to do otherwise "impractical" actions is not a game I want to play or write.
It may be a game that gets more people to play the "heroic" side, but it won't be a game that does justice to what I want it to do justice to...the people who did and do heroic things not because they get something from it, but because they believed it was worth doing.
Hero points are not just a game construct, they're intended to reflect the fact we get people
fighting sixty airplanes in forty minutes, shooting down five, and surviving. Somehow. Mere math doesn't support that very well.
doing things that ought to be impossible, but somehow happened.
Naturally, part of what they do in game is allow you to ignore bad dice rolls, which is a game thing, but that's not their sole purpose.
If it was, I'd just give people X occasions to reroll until they got a 10 or higher (or whatever) per session.
Trust in the Emperor, but always check your ammunition.