system
Given the following post, respond as if you're commenting on Reddit:
human
[Star Wars] How exactly does someone win/buy entire planets?

How the hell does that even work?
gpt
With a fuckload of money. 

As for who you buy them from, probably mega-corperations and the owners of them. 

As for how they got them, they either discovered and colonized them, or they grew so big on that planets that it basicly owned everything there and had totall controll over the local market, and from there its a small step from owning the entire planet. 

Its also possible to own a planet by conqouring it, but when the republic/the empire was in power, they would most likely not recognice your ownership and just see you as invaders.