If you are an ally of a defender your part in it only lasts a week and then you need to re-ally. that’s kind of mindblowing, and useful all in itself (that you’re not stuck in if it goes bad)
eve university doesn’t mention this - Corporation diplomacy - EVE University Wiki
ccp obviously didn’t mention it (i guessed) - https://support.eveonline.com/hc/en-us/articles/115004152745-Wars
the forums didn’t mention it (troll cesspool) - Search results for 'war defender ally' - EVE Online Forums
i asked in help channel nobody knew wtf i was talking about
here’s two pictures of what it looks like right after that 1 week
aggressor - https://i.imgur.com/CcNgw9H.png
defender’s ally - https://i.imgur.com/pgsE7Oc.png
here’s the picture of what it looked like when i made the video
defender’s ally - https://i.imgur.com/e39VmJQ.png
CAVEAT: video was made when i thought i found a weird bug, and possible exploit for ending a war prematurely. this forum post here in the general discussion is my followup to that.