Inverted: Carl turns up to encourage Alice and Bob to fight one another because he is a spy working for Emperor Evulz.
Subverted: Carl shows up and announces that the war is all a scheme by Emperor Evulz. The armies ignore him and fight anyway, because they don't know who he is or don't care.
Double Subverted: However, Alice and Bob do and order a halt to hear Carl out.
Parodied: Alice and Bob stop their war campaign at the request of Carl, an ordinary person neither of them have met.
Zig Zagged: Carl manages to stop Alice and Bob from slaughtering each other at that battle, but the two keep fighting anyway. It takes an attack from Emperor Evulz for Carl to get his message through and get the two to cooperate.
Averted: Carl doesn't try to stop the fight.
Enforced: "We have to make Carl do something cool, but he's an Actual Pacifist. Let's have him stop a war."
Lampshaded: "You'd have thought Alice and Bob would've been more careful if they were willing to stop the fight."
Invoked: Bob is fated to help stop a war, and since Bob is not a good warrior he decides to follow his destiny peacefully by encouraging diplomacy.
Conversed: "What do we do about Alice and Bob?" "I'll jump in between them to stop the fight and get them to listen to me. After all, they both know who I am."
Carl, who Alice and Bob see as True Neutral, is not prejudiced to favor either side and so they are willing to listen to him. Since neither of them are really bloodthirsty enough to fight a pointless war, they call a truce under his advice to battle Emperor Evulz.
Alternately, Carl's idealism reminds Alica and Bob that their war is pointless and will end up causing much more destruction than good. Witnessing an act of simple, selfless courage gets them back to their senses.
Reconstructed: Bob and Alice suspected Emperor Evulz, and only fought each other since the other ruler's army was the more immediate threat. Learning that they were used makes them angry and more keen to fight Evulz instead of each other. After Emperor Evulz is defeated, Carl constantly has to find a greater enemy to battle to keep Bob and Alice from fighting.