Reply #1 from Stardock Forums Top

The general idea is that space is very big and you are allowed to go into other territory but they don't like it.  There is a diplomatic penalty for it.

Moreover, those games either have very small (relative) borders or star lanes.

Reply #2 from GalCiv4 Forums Top
Quoting dynia666,

why this game don't have closed borders optioin  like any other 4k games like stellaris or civilisation 6?

End of dynia666's quote
Quoting Frogboy, reply 4147576

The general idea is that space is very big and you are allowed to go into other territory but they don't like it.  There is a diplomatic penalty for it.

Moreover, those games either have very small (relative) borders or star lanes.

End of Frogboy's quote

I just put a starbase and on the end of a stream the AI must go through (on the AI's side) and block all the other hexes with warships.

Then I set my map up so I have a sector that is all my own

This blockade method would work also if you eliminate all the victims located in your or additional sectors 

The blockade is on the AI side as the AI will run a ship through a stream not be able to exit and blockade me instead 

Have to either go to war or steal err I mean trade for the ship it stays in the exit hex "inside" the stream

Siege of Centauri