Missions are procedurally generated based on current state of affairs in the system and surrounding area.
For example, a lawless pirate base will often have plenty of pirate missions where you have to "procure" certain goods. Or a system at war will often have warzone kill missions. Sometimes you can actually find more warzone kill missions in *surrounding* systems (depending on the faction allegiance) than the one actually at war.
Courier missions, which you did, are also procedurally generated. They do have an impact (you can see the summary after you complete the mission), but do not expect to start a revolution by delivering a pamphlet or a secret message. It would take many players quite some time to visibly impact the state of a single system - after all, you're just one ship, there's millions or billions of people living in it.
What you do impact the most is your own reputation with the factions. Friendly factions will be more inclined to offer you much more lucrative missions, so it pays off to work at it in systems of your choice.