*Cough cough* as a ruler you can set this though.
In the kingdome menu there is a setting to let you choose "balanced" "defensive" or "agressive" or something along those lines, you can set your clan-parties to similar styles.
I'm guessing if you inherited it from Derthert he prolly have it on "defensive" due to his "cautious nature" if its set according to his index-entry.
So try to check if you have it on defense, and flip it over to whatever you want it to be.
When I was king in my play I had it set to the balanced one, and my faction was raiding all the time when not in armies.