I like an idea i saw before where offensive war alliances are a one time deal made seperately for each offensive war (which could I guess benefit from having a long standing defensive alliance). while the current alliance mechanism is changed to only be for defensive wars
it is pretty annoying you can't join an ongoing war. sometimes even because the AI failed to call you in due to some chain of alliances shenanigans even though you were their ally. I had a time or two where i was supporting independence, but then the independence war somehow happened without calling me in and I couldn't join. they lost, and then I couldn't support it again because they didn't have the liberty desire anymoreAsk to join war would make this one of the best patches ever. Add in a way to soft call to arms without the alliance breaking if refused for offensive wars and we're looking solid.