I'm currently in the mid-game of Stellaris and building up a pretty big empire. From beginning on I had three neighboring, strong empires. I've beaten two of them recently, and forced one to be my tributary and the other one my vassal.

Now I would like to conquer my third enemy...but in the war conditions menu I cannot choose to vassalize him. I can only make a tributary of him. Why is that?

I've also checked some other (small & big empires) and it seems that I cannot vassalize any of them. I can only choose the tributary thing in the war conditions menu. Can I only have one vassal at a time? I've integrating my vassal at the moment: does this affect the vassalization of other empires?

2 Answers 2


You can vassalize by liberating a group of systems, then vassalizing the resulting empire formed of those systems. The new empire that's created as a result of Liberation has a large bonus to their opinion towards you because of the Liberation, so you should be able to vassalize immediately.

If you have a Defensive Pact or higher (Alliance, Federation) with another Empire, or they are a Protectorate, you can't vassalise that Empire.


Is it possible that the empire you're trying to vassalise is too large? If the required warscore exceeds 100, the system won't let you declare war.

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