How can I make the barbarians loot more frequently?

[nihahahahachang]

I have once been surrounded by many of the barbarians, but they just suicide-attack my city and do not do any harm to my improvements. So they have just become some kind of guards for my civilizations and the beeing which reduce the happiness of the game and reduce the difficulty.
I wonder if there is any tools for me to use to improve the favour of the barbarians to loot the improvements?

 

[nihahahahachang]

what's more, the navy of barbarians never blocked my coast.

 

[45°38'N-13°47'E]

If you play with Raging Barbarians, upcoming Rev1054 should improve their activity