system
Given the following post, respond as if you're commenting on Reddit:
human
[The Expanse] Why aren't Belters UN citizens?

They had to come from somewhere, they weren't fabricated in space. There doesn't seem to be any indication that their ancestors were legally exiled and stripped of their citizenship or voluntarily renounced it. They just moved to space and a few generations later there's a pseudo-slave underclass with no rights. How (not) on Earth did that happen?
gpt
As soon as stations like Ceres and Eros became semi nation states, run by corporations, people born on them no longer qualified for citizenship. They probably had some clause saying "must be born on Earth, Luna or a UN ship/colony". So if a belter accidentally popped out a baby in the UN Embassy on Ceres then they probably qualify.

Furthermore there was probably political tension caused by the UN trying to claim all those born throughout the belt were UN citizens, Mars probably had a fit saying some of them were theirs, in the end they probably just agreed to leave them stateless.