Granularity - the extent to which a system is broken down into small parts.
Does your world have functional granularity? Do you worry about trade between nation-states? Lots of games start with the premise of a trade route being disrupted or being ended (most of the time it is a vital substance and there is only one route). Responding to this plot hook, players tend to fall into two categories, those that question why event X needs to be addressed and those that question how to resolve event X. Aside: the groups that I game with fall roughly even on each side of this line, with many of the more experienced players asking the why part.
So how do you deal with these questions and get the party moving toward figuring out how to resolve event X? Use an NPC to give them the answers, then give them the likely outcomes of each solution as seen from the NPC's perspective, but whatever you do, don't punish them for not doing what they are told is the best solution and don't reward them for doing exactly what they are told - think the opposite of Pavlov's dog.
What about when the party is not exactly good and decides to become raiders themselves? Well, for one, make sure you have some valid trade routes and goods to be raided. Also make sure there is some sort of militia or police force that protects these trade routes, otherwise why aren't they being raided all the time?
There are quite a few things to remember when a campaign moves in this direction. What are the punishments for being caught raiding (both stealing and possibly murder)? Is there a justice system in place or do the locals just take care of the problem? What about if the raiders have "permission" to raid certain goods or attack certain traders but not others? How fast does word spread of a specific trade route getting hit regularly? How long can a route be raided before the traders take matters into there own hands or force the governments to get involved?
If you cannot answer these questions, then your game lacks some necessary granularity and you may want to rethink putting the players into this type of story arc.