Humans are all dead and only zombies are alive who have now turned on each other for food. You're one of the zombie factions and must destroy others to survive now.
Instead of building towers and defending against hordes of monsters, play the opposite as an evil mage that builds his army from the ground up to dominate the lands.
Build structures, train army, destroy enemy castles. Your soldiers will charge and break through enemy defense lines automatically and use magic to assist your corps assaults.
Build your creature army to overthrow the King! Total of 28 different creatures. Each of them has different abilities so try to combine them effectively.