Why do raiders always *attack*? I mean, having the occasional group of psychotics is one thing, but this is *every* time. What ever happened to extortion and negotiation? Do they really just want to kill us all, or do they want our stuff. I would (often) give them some stuff, if they would then go away at least for a while, if they only asked.
So you would want something like they contact you via the comm console and force you to pay money? If they don't pay then there's a good chance (not guaranteed) that they'll attack?
Or they would steal from your stockpiles possibly, either silver, food, meals, etc? And you could engage them?
Maybe even clean rubble off your floors because they're mad? 8)