Tell me, if you were the leaders of a state, would you agree to sign an agreement with another state, that says that if your ally declare war on anyone, no matter who, you are with them in this war? Even without them notifying you a minute in advance?
Also historically, I do not remember such a kind of agreement, except for vassals, protectors or another type of puppet-state.
But in Total War Campaigns, there is a diplomatic option, called a "military alliance," which means just that.
I think in the next games of Total War, this option needs to be improved. When I play, I almost never want to sign a military alliance. But after the factions who like me drive me crazy almost every turn to sign a military alliance with them, I finally give up and sign, and then regret it.
Likewise, even faction, who has many military alliances, can declare war on you - and suddenly you discover that the whole world is against you without any prior preparation.
The issue of reliability is also not clear enough. It must be clear to the player: What happens when I betray the agreements I have signed? What price do I pay? And in case my military ally declares war on whoever has a defense alliance with me, with whom should I go so that my reliability is not harmed? The answer to these questions should not be clear only to those who have accumulated long hours in Total War games.
I also do not like the diplomatic option "join war against", it means that a faction can actually declare war on me on the one hand, but also avoid war against my defensive ally on the other. It must be that if anyone wants to fight against me - he will also declare war on my defense allies.
Speaking of diplomacy, there may be all sorts of diplomatic options, while switching cities, that in some Total War games they exist, and in some not. I think, the more diplomatic options there are, (that makes sense!) The more fun the game. Do not think so?
I would like to see the next Total War game, Warhammer 3, full of diplomatic options. At least like TW 3 Kingdoms.