So I decided to colonize near a Fallen Empire. They were fellow spirituals and were sitting there for some centuries already, what harm could there be in it, right? And everything indeed went well enough, until out of nowhere they decided to become an Awakening Ascendancy, tried to make me a subject and declared on me shortly after I refused.
They were demanding me to tear down half of my border outposts, cede a whole bunch of planets and a whole lot more, and to make things worse for some reason we(me + federation) were considered the aggressors even though we were the ones who were declared upon.
They had like 2 60k fleets while my federation had a total of ~30k that couldn't coordinate for shit because paradox AI, I really thought it was game over for me right there. Until, after occupying some 4 of our planets, they just sat there doing absolutely nothing for months, maybe years. The resource drain hit me pretty hard and I had to tear a good chunk of my fleet and stations, but I managed to survive until they used their 30% warscore to make a fairly mild demand to cede one planet(a really good one though, RIP) and give up a couple of border outposts.
So, wtf was that CB that allows the declarer to be the defender and does it happen often that the AI simply stops pushing when they could easily lay waste to the whole enemy territory?