I think this is a problem unique to starter alliances (0 cups no invite types).
I think a lot of new players make mistakes when they play their first war - they don’t realize what they are getting into, and then don’t realize they are automatically in future wars until they opt out. I think some sort of follow up prompt would help after the first war.
For example:
“Would you like to participate in all future wars (you can choose to participate at any time if you choose no now)?”
The problem for starter alliances - if you have a “use all flags requirement”, and they can’t, not a big deal, they figure it out, that’s how you learn, but then next time they are in war and may not even realize it, and then it becomes a problem for the alliance - do you kick the player to stop them from bringing the active players down or keep giving them chances?
At least if there was a follow up prompt they would realize they needed to opt out or that they were opted in, I guess. This is similar to other war requests, but I think an alternate way of handling it.