Eliminate the guardians of the capitals.

I bought (or rather, stole) a bunch of defense potions – the yellow ones that give +50% defense are great, plus spells. I last played as the Empire. They have good defensive spells. I cast them, and then I go on the offensive. But before sending my army to attack a castle, I buy a ton of thieves))))) and send them in first... At least six of them definitely did their job)))) One of them even killed a possessed creature standing in the first row. After I conquered the castle, the demons stopped bothering me by encroaching on my territory anymore. But I think the computer was probably in shock))) Players aren't supposed to capture castles)))))