Kingdoms & Lords

To defeat the Barbarian General, you need to win 3 sets of 3 fights against his armies for a total of 9 fights.

Tips:
If you already unlocked (or bought) a stronger version of the unit I recommend, use that one.
Upgrade your units in the Training field. Each unit has 7 different skills. 6 skills cost coins and resources, the 7th costs diamonds. (Diamonds are a rare resource, spend them wisely.)
Magic cards, especially Flame strike, can help you a lot.
Mona can help you too, replace a unit with her.

Reminder:
Enemy with green up arrow means you do more damage.
Enemy with red down arrow means you do less damage.
Enemy with no arrow (unit icon instead) means you do normal damage.

The first fight of the first set will grant you:

1st set:
1st fight: (2 energy)
Barbarian General:
- 2x Axemen
You:
- 2x Spearman
- 1x Swordsman

2nd fight: (2 energy)
Barbarian General:
- 1x Axeman
- 1x Spearman
You:
- 2x Spearman
- 1x Swordsman

3rd fight: (5 energy)
Barbarian General:
- 1x Swordsman
- 2x Axeman
You:
- 1x Axeman
- 3x Spearman

2nd set:
1st fight: (3 energy)
Barbarian General:
- 1x White Knight
- 2x Swordsman
You:
- 3x Light Cavalry

2nd fight: (3 energy)
Barbarian General:
- 1x Swordsman
- 2x Spearman
- 1x White Knight
You:
- 5x Light Cavalry

3rd fight: (6 energy)
Barbarian General:
- 3x White Knight
- 1x Swordsman
- 1x Spearman
You:
- 5x Light Cavalry

3rd set:
1st fight: (4 energy)
Barbarian General:
- 1x Spearman
- 2x Light Cavalry
You:
- 4x Dark Knight

2nd fight: (4 energy)
Barbarian General:
- 2x Spearman
- 1x White Knight
- 1x Light Cavalry
You:
- 3x Light Cavalry
- 2x Dark Knight

3rd fight: (7 energy)
Barbarian General:
- 1x Axeman
- 1x Swordsman
- 1x White Knight
- 2x Light Cavalry
You:
- 3x Light Cavalry
- 2x Dark Knight


You have now unlocked the possibility of hiring the Barbarian General in the Hero's tavern for 40 diamonds. (Diamonds are a rare resource, spend them wisely.)

Note:
Lots of different combinations of units can work just as well and you can use whichever you see fit. This guide is only here to help anyone who is stuck on a specific fight.