I signed a peace treaty with the Outlanders, because I didn't know how to invade their planet and now everyone is neutral :)

Well, not being in war with everyone is better, right? :)

For planetary assault, you should fully research the Proxima, build it and send it to the planet. You will have to defend it while its weapon is charging. I will link you TheRevPlays tutorial guide where you can see how it's done.

This is a livestream but it shows the planetary assault. Proxima starts at about 25:00

https://youtu.be/4S_p-YVraJg

I may just finish the campaign then, don't want to spoil myself :)

Still hunting for parts to build that ship/station...

Hmm, I did use the hostile terretories to expand the Empire! Now I have to declare war on my next neighbour...

After the failure to take over Gemini, we need to rebuild and show those rebels who is in charge around here.