To win combat in Fortress Kings, you have to exceed the defenders defense values with your units attack values. This means that the defense stats of your units are irrelevant when attacking and vice versa.
Your units attack and defense values are split among three combat categories and the amount of categories required to win depends on the type of attack.

 

The are three combat categories: infantry, artillery and cavalry. Your units have attack and defense values for each of these categories. All units belong to one of the following unit-types:

 

Units excel at the combat category their types correspond to, with the exception of the „Special“ and the "Mercenaries" category.

Units that belong to the „Special“ category are traps that cannot be used to attack other players, can't recover in the military hospital when destroyed, but have high defense values. Spies are an exception to this, as they cannot participate in combat and are used to gather information.

Raiding only requires you to win in one combat category. When successful, you will steal resources from your opponent. At most 20% of units on both sides can die.

 

Conquest requires you to win in three combat categories. When successful, you will swap positions with the defender. At most 50% of units on both sides can die.

 

Liberating requires you to win in three combat categories. When successful, you will free the attacked building. At most 50% of units on both sides can die.

If you lose a battle, you generally lose 50% of your units. If you win, you lose units based on the strength of your units compared to your opponent's.

For example if you win with 200 attack vs 100 defense you lose 25% of your units.

 

You can only damage your opponent if you reach at least 2% of your opponents combat strength or 1 Million attack in at least one combat category.

In other words, if you are 50 times stronger in a category you will not lose any unit of that category unless your opponent has at least an attack value of 1 Million.

 

After an attack, your units will need to recover for a period of time depending on how many units you sent. While recovering, units cannot defend your castle, nor can they be used to attack.

 

Units that are defeated in combat can be recovered in the military hospital if there is enough space available.