Since the beginning of time, war is among the best way to gain wealth. However, it comes at a deadly cost, so nations become friends. Soon, all of them prosper and become rich. However, upon the coming of the undead, alliance has been broken because some of them have sided with the undead for protection. You need to liberate the nation against the undead. You need to takeover some castles to win in each battle. As you make some progress, you would unlock some new skills. You need more money to hire more troops, so build those mine first.