See, the idea is that the players are technically fighting for the wrong side. Both sides are arguably bad, but their side is worse. They were the aggressors, and the monarch is under the influence of a devil that's looking to escalate the war as much as possible. To my mind, the PCs should eventually figure out that something is up, and look for a third way to bring an end to the conflict.
The thing is, the PCs just enjoy what they're doing too much. The party leader is probably the worse offender. What happened is that, at one point, they captured a group of guerillas looking to sabotage their weapon supplies (including cannons) and prepared to herd them off to imprisonment. They actually killed most of the fighters, so the reminder were obviously pissed, but an important NPC (the future resistance contact) was amid the group of fighters.
The problem is, the PCs didn't even speak to them. They just prepared to send them off to the labour camps. In an effort to put more plot into the story, I had the guerilla leader go on an exposition rant about the atrocities their side had committed, and how they were fighting for the devil himself.
So the PC leader said "Wait, I've changed my mind. We're not sending them off to the labour camps." But instead of asking exactly what the fuck she was talking about, he said "Hang them."
Anyway, I called the session for the evening. I didn't want to break kayfabee, but I told the leader's player that "Hey, maybe you should look into things. That person might've had a point."
The PC told me "Oh, I know something's probably up, but I don't really care. I'm not interested in helping them in any way, I just want to win the war." This is a problem, because the other PCs just sort of go along with whatever the leader (who is, to his credit, the one most invested and interested in the setting) wants them to do.