"Frida's Dilemma" - "Negotiations" [Campaign 1, Mission 4]

Also, all the units of the Haven faction will join you, and there are a lot of them. If you collect the dwarven artifacts, you'll find paladins in the dungeon, and they'll join you in exchange for these artifacts – 45 of them! With such an army, you can defeat anyone, just don't give them to the mage in exchange for showing you interesting places.