I originally posted this on Reddit and was advised to post it here. Please excuse my frustration with this situation.

I'm playing as Unfallen and going for Supremacy victory. I can't occupy the enemy planets unless they are vined so I'm just razing everything. I've wiped out the Vodyani, Cravers, United Empire and I have the Sophons, Riftborn and Horatio as my allies. 

With my alliance that puts me at 4/8 planets for Supremacy and with Vodyani, UE and Cravers destroyed I am at 7/8

I wiped out 99% of the Lumeris too, including their homeworld, so their capital got relocated to some back water.

Now heres the problem... I'm 7/8 for the supremacy victory condition and the Lumeris final planet is at 0 / 1250 defenses with a 2x 24 Sophons fleets outside it and a 24 Riftborn fleet as well as one of my 24 fleet cap fleets.

I can't invade the planet because it says "This system is being guarded" and even though its 0 / 1250 defenses neither the Sophons or the Riftborn will fucking invade it or stop guarding the planet. I can't break alliance with them because that will put the victory condition way back down to 5/8

This is honestly so stupid. The system can't even defend itself and they won't invade it. It is literally the last move of the game. 200 turns for nothing, at this rate. 

I won't be going back to that save but I think that Amplitude definitely need to look at the AI in this situation because they were literally the only thing preventing the game finishing. Why wouldn't they just invade the planet? It had 0 manpower left on it. Really annoying.

I don't have the Supremacy DLC so I was not able to just use a planet cracker to bust the planet open as someone else suggested.

Maybe they saw something in the Lumeris that they didn't want extinguished. Or they might think your quest for galactic conquest has gone far enough and are holding off in protest.

SpaceOrbs wrote:

Maybe they saw something in the Lumeris that they didn't want extinguished. Or they might think your quest for galactic conquest has gone far enough and are holding off in protest.

While it's all fun to have a joke, I don't think you'd be as amused if it happened to you :-) 

My allies were all pissed off with the Lumeris too, and the Lumeris were causing my allies much more trouble than the Lumeris were able to cause to me. 

They were annoyed enough at the Lumeris to siege their planet out and blockade it but not fully invade.

It definitely was not normal AI behaviour.

Could you please provide a save game for us to take a look at?

Happy to provide the save - not exactly sure how to go about it though. Do you have any instructions?

Go to Documents\Endless Space 2\Save Files & find the name you saved or check the time the savefile was created

I just leave the alliance at that point. Granted it is fun to be able to use all the science victory techs without immediatly winning.

Isn't Supremacy supposed to trigger when you control the original homeworld? Their backwater relocation shouldn't matter unless you're going for Elimination.

In any case, when all else fails, blow up the planet.