For me, since I mainly play as Barbarians, diplomacy is a very useful skill! It's almost a must-have for Barbarians; you should take it as early as possible to conquer nearby mines, which speeds up the construction of their castle, which is already built quickly anyway. And sell the remaining armies to the Guild of Workers to further accelerate construction. Another useful skill is artillery. Take it with your second hero and place them to defend the castle. With towers and everything else, you can destroy archers and ballistae, and then you can consider the city saved! If not, in the case of Barbarians, you can escape through the secret passage, hire a hero in the second castle, give them the army that was captured thanks to the diplomacy of the first hero, and calmly go and take the castle back. In general, I always take Wisdom and Earth Magic. The "city portal" spell is very useful in a strategic sense.