HOwever when alien species join the federation and their territory have many pre-warp civilisation, I can see it problematic
Perhaps the prewarp civilisation planets are not considered part of federation but the region of space outside a certain radius from the planet (or let say the entire solar system) is not considered part of the FEderation and considered neutral space. PErhaps there are pockets of neutral space within Federation territory
Itís pretty immoral to claim space when there are other species living in there.
The problem with Insurrection is that they mentioned that the reason why Sona was interacting with the Federation because the planet is inside Federation territory. They also mentioned that Baku arenít native to the planet. So the logical conclusion is that they are squatters on Federation territory and they have every right to kick them out. However Iím sure the writers donít actually mean that but itís so poorly explain and no clarification regarding that point. Maybe the planet is neutral territory or territory of the Baku but requires crossing federation space to reach it and thatís why the Sona were negotiating with them but thatís me filling in the plot hole for the writers