Questions about political borders... IN SPAAAAACE! (and some other stuff)

How would political borders work in space? I'm currently treating interplanetary space as ocean and planets as landmasses. A polity has complete sovereignty over their planet and its gravity well. For large planets, the space occupied by the planet's orbit is also considered an exclusive economic zone. foreign entities may travel freely through this zone, but may not exploit resources found there or set up permanent orbital colonies there.

I suppose I'd have to look at what a polity is capable of defending militarily, since practically you can only keep what you're capable of defending from rivals. A planet's surface and gravity well are easily defensible, but I'm not sure about the entire orbit. Planets move around relative to each other.

The yinrih are also quite fond of building massive spaceborn archologies that are nations unto themselves, though they are much smaller than planets and don't have a significant gravity well.

There are two polities that require special consideration, The Spacer Confederacy and Partisan Territory. Both are collections of these spaceborn archologies occupying resource-rich asteroid belts[^1].

The Spacer Confederacy is a loose collection of independent city-states that somehow hate each other just little enough to form a federal council and police force to protect the common interests of the inner belt. Partisan Territory occupies the Outer Belt and has a totalitarian system of government.

Here's story that explains a bit of how the Spacer Confederacy works. I'm not sure how viable such a system is, but if it doesn't work, I'm hoping it "doesn't work" in a way that allows for more interesting worldbuilding rather than just being stupid.

[^1]: Yes I know the IRL asteroid belt has a tiny amount of total mass, but this is my world, dang it!