Thanks for replying. I replayed those turns and yep, war occurs without any declaration. This is a map with nothing but custom civs, some AlientGPT and some my own, and when . . . wait for it . . . the Moties wipe out the Borg (sounds legit), then I'm suddenly at war with the Moties without anything except "The Borg have been destroyed" and my reply, "Understood" popup.
Here's the save game. The Borg get blowd up in April 2324, so a few turns after this. I can get to the exact moment and save, but I unfortunately neglected to keep saving after every turn for some reason and this is as close I have at the moment. Hope this helps.
(Side note: can we also not let unarmed probes start fights? It didn't happen here but it occurred to me as an example of where you don't get the civ picture war popup and "your planets will look better with our banner over them anyway", although you DO get the "do you want to I dunno crash into these guys and start a war?" smaller popup.)
https://drive.google.com/file/d/16ex9W5F1Sm6-FWOFdvVRuH8geAJqAcED/view?usp=sharing
