You could have a CPU villager constantly cutting wood until reaching an enemy army and tweak the personally to make it retreat to the other army, start a battle that the other army can't win. Dead bodies.
With this, the timing is crucial. You have to expect people playing this scenario to get to a certain location by a certain point. So one way is to have larger armies, so that the fight between them will take longer, produce more bodies, etc.
Alternatives
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-Closer to player's location.
-Cutscene, Invisible Demons on a battle field, set it so you win when the player that should win, wins.
-Cutscene, Invisible Demons on a battle field with bodies rather than armies. Set up a CPU gathering berries in the corner constantly and the scenario ends (Player 1 Victory) when they get a certain amount of food.
-???
-Profit.
[/Your Reign]
Take that, Player 2!