Can't ask for alliance...EVER

[Omanes Alexandrapolites]

Hmm, sorry to disagree TruePraetorian, but I'm not sure if that is the case. On many occasions, I have aligned with a faction who my ally is at war with. The ally then sensibly concluded their alliance with me and continued fighting. I have seen it go the way you have described though, which probably indicates that the AI has a choice on whether he wishes to retain friendship or not.

I believe that if the faction is someone that one of your allies is at war with, you can't offer an alliance.

I don't think that is the case, although no research has gone into the disappearing alliance button. I have daubed it a bug, but more experienced players may be able to confirm it as something different.