The Trading City that I am asking is major powerhouse of mother river.
The setting is a pre-industrial post-apocalypse world where there is no magic. This trading city is ruled by Srbiyan soldiers who colonized this city 100 years after the doom when the Srbiyan government decided to conquest more land but those soldiers took land for themselves. They have interbred with the natives after they arrived and settled down.
The labours and workforce of this town, and other towns nearby, are Palmajeese immigrants that migrated from Moonshine. They worship the God of Moon and are nomadic after the doom destroyed their country. But Bratibor (the city name) relies on the Palmajeese slaves for everything; they have become decadent but at least they can shoot slaves, and the reason that Palmajeese never rebelled was because they have nowhere to go as all surrounding towns are also slaver cities. They also have strong a cultural loyalty towards their masters and even worship their masters because they think that they are saviors.
Meanwhile, on the opposite side of the river there is a long pipeline that has been abandoned after the doom was gone and now the oil is leaking. The Pipeline and area around it are "Lou badland". That area was the most rural area of confederate of Lou (old colony of Valoria that is kinda like America) and is now settled by various Lou tribes that considered themselves the "blood of Lou". The reason that Valorian colonized this land was because they have oil, not because they are Lou (the Valorian ancestral tribe).
The Badlanders (these tribes) have some guns from the pre-apocalypse era and some handmade guns from northern Lorian. They used to live at riverland but the Lankrin took riverland away so they migrated to southern land.
I am trying to come up with an answer for why the Bratibor (the steampunk city) do not invade the badlanders, considering they have oil and workforce and they are weaker and less organized than Bratibor armies.