It’s well established in both the canon and the EU that the core worlds have always been exploitative of the outer rim. The earliest example of this (in terms of in-world timeline) is the conquests of the old republic into the outer rim during the sith wars. In essence, the core worlds represent the first world of IRL and the outter rim represents the third world.

During the Republic, it’s already well established that the republic only worked for coreworlders and humans, this is reinforced by the opening negotiations scene in episode 1, and further reinforced in nearly every examination of the CIS that attempts to explain why systems joined it. I don’t off the top of my head remember when this was added to the canon, but it was before episode 1 and sometime after episode 7. But, we also see with the New Republic, they kinda just reverted to this exploitation of the outer rim.