Rock, Paper, Scissors!
Here is a very important thing to know about attacking and defending. This game uses a RPS (rock paper scissors) method of determining appropriate attacks.
Melee troops are one of these types. For instance, a Spearman is a rock type troop. It is best against a scissors type troop and gets an advantage in the attack. It does more damage than a same sized paper troop would have done against a scissors troop. Attacking with the wrong type gives a serious disadvantage to the attack.
Spearman Rock Type
Swordsman Paper Type
Scout Scissors Type
Plan your fights with this in mind. You'll need all types to face an uncertain future!