Only a good team work can save the kingdom. Place your battle units on the same lane with your enemy and let them do the job. Defeat them using some sort of magic and collect different bonuses.
Get ready to defend your lands against the hordes of various enemies. Look at your current mana and place soldiers to prevent your enemy from reaching a key point. Keep some mana to place another soldier if your current soldier dies, beat your enemy and collect gold from their corpses. Free your lands and proceed until the kingdom is safe!