NPC annexing core worlds

my first run an npc civ declared war then simply took over my planet without so much as a battle or even a notification from the game at all.  I only found out because I noticed my home planet had changed color on the map

my second run the npc civ didn't even have to declare war - the npc civ simply began annexing my core worlds regardless of approval levels - no war, no rebellion, they just began annexing all my planets with no explanation or justification.

this game is looking worse every run