Economy and Political Stances
These resources can also affect political relationships. An area poor in a specific resource might have a strong trade relationship with another world that has it, or they might rely on conquest and war to plunder what they need! Settlements also disagree about political structures, public policy, religion, and any number of other factors.
You'll also want to consider the significant NPCs of each settlement. This includes the official rulers, but it also includes other major players, whether they act in an official capacity or entirely behind the scenes.