The first thing to understand about how to have NPCs with legitimate grievances be a thing in a TTRPG is to imagine the world as a real one and the NPCs as people within that world. If you're just thinking of the setting as a flat backdrop for gameplay and the NPCs as colorful questgivers whose protection is a thin excuse for the plot to happen, then you're not going to be thinking in terms of things like what needs various NPCs might have and why they're unfulfilled or violated.