Back in 1.1 I played a game of fanatic xenophobia where I purged everything in a tiny galaxy, funnily enough I've actually been a protectorate of a neighboring advanced start empire (with exact opposite ethos - fanatic xenophile) for quite a bit. Since there was no way I could've defeated him in early-to-mid game due to him being far superior in tech I demanded protectorate status. Not sure how much it has been changed since then (I assume a lot), but back then it was incredibly OP, since anyone who would've declared war on me would have to fight the overlord empire as well, while I was free to expand (and purge) as I wished. So while the overlord was busy fanaticaly colonizing every planet he could find in his half of the galaxy I was busy fanaticaly purging everything in my half. Eventually there was nothing left but me, my overlord and some of his other protectorates. By that time I catched up in tech, built a superior fleet and declared war for independence. Since you could've abused truce timers by declaring wars on vassals back then I was basically at non-stop war with him ever since.
Never been someone's non-protectorate vassal though. I wonder if the AI will try to integrate a vassalized player empire.
So its 1.4 Kennedy now, my first REAL game of stellaris after a couple just playing around with mechanics, getting a feel for the game.
I am the Imperium of Man, and I suffer not the xenos to live. The xenos try to resist ofc, making a federation of literally like 60% of the galaxy against me, but petty internal squabbles and xenos politics could not stand before the might of my armies, and I now own a solid 1/3 of the galaxy. So, its late game now, and I've made no progress. Why you ask, because The War in Heaven. So, I kinda spawned next to a xenophobic fallen empire, and on the other side was a xenophilic one. long story short, they went to war. Now, the problem is that the first thing the xenophobic empire did was vassalize me. Yes, to my shame I am now the vassal of another empire (mostly cause i had 50k fleet strength left from war at the time, and they had 150k). The xenophilic allied with most of the galaxy, including the federation (my rivals). The war caused the Unbidden to spawn, and the war ended in a tie. Now my overlords have 300k fleet power, i only have about 150k and the unbidden have literally eaten 1/4 of the galaxy. I have taken the Xenophilic empires homeworlds, and basically removed them as a threat. The problem is, I have no idea how i am going to win now. I cannot fight my overlords on my own (300k > 150k) and everyone else hates me (apparently i am a "fanatical purifier). I cannot declare war on the federation, because they are still technically vassals to the xenophilic empire, and I cannot declare war on anyone else because they are the vassals of my overlord. What do I even do in this sitution.