There are 4 prospered cities in the middle of the kingdom. These cities are literally prospered resource villages. They will do crucial role in filling your storages once you occupy them. Send a hero to an empty one and occupy it. If there is already a person who has occupied it, there will be a battle, but still it is worth the fuss; you should prepare for the battle and go for it, as the person will be more powerful eventually—which you have to prevent.