Ok, I can't remember the name of this story, but I remember some of the plot. Humans, or the species the main character's from, take over a planet, but the locals are pretty chill about it and just go along with it, which confuses the main character. The basic idea that the Main Character learns is that the planet had been taken over before, but the race that lived there just went along with it and the 'conquerors' basically melted into the culture there. It happened before, and the main character saw the evidence of this through their currency.
I also remember that the native species kept track of time through generations, not through actual years.