You must complete the missions up to the one where you have to choose between "To Loren", "To Zhufbar", or "Revenge". Choose "Revenge". You must win as much as possible and recruit the new armies. Then, go to Zhufbar and win the ambush. When you get in the town, ignore the crossbowmen. Go to Zhufbar. Once in the next town, do the farmer mission. It is very easy. Next, get to Zhufbar. Once there, do the "Listening Gate" mission and select everyone to go with you. Have everyone go to the gate except for the cavalry and wolves. Send them to the top-most army, next to the rock thrower, and have them attack. Then, have everyone get to the gate. When the dwarves get to the gate, it opens for a limited time or until an enemy gets near them. Make sure to have everyone at the gates when the dwarves get there.