I like that the game gives you the option to turn a minor regime into a vassal if you so desire, instead of just conquering them by force. However, I was kinda disappointed with the feature when I tried it.
These are the problems I found with the feature or at least areas where it is lacking:
1: There only seem to be 3 minor regime stratagems in general.
Propose peace, make protectorate, make vassal. If you tell your foreign affairs director to focus on diplomacy with minors, you will eventually build up a huge stockpile of these cards, more than you're gonna be needing of them. None of these cards are really reusable or applicable to many situations.
More reusable minor diplomacy cards would be nice to have. Maybe something like a card to bully them into giving a one time tribute or to influence them into attacking one of their neighbours.
There should also be a card for improving your relations with minors. Right now, if you fail the roll to turn them into a protectorate or vassal, then they will lose some relations with you and there's pretty much no way for you to make this relation rise again, unless maybe if you get some random event.
2: I think it would be nice if there was a third foreign affairs investment slider (besides major and minor diplomacy), a slider specifically for diplomacy with your subordinate regimes, protectorates and vassals.
These stratagems could be things like, asking them for money, for militia units, for leaders, to attack some other regime, increasing relations, slowly trying to integrate them into your nation.
I'm imagining it something like this: If you play cards asking for favors like money, militia units, etc, then they will reduce your relation with them even if they were successful (maybe not on a critical success?).
If your relation with them drops too low, there would be a chance for them to break free and stop being your subordinate.
To counter-act that, you have to play other cards that increase your relation with them, so that your relation with them pretty much becomes some sort of currency that you get to spend on favors.
I know that subordinate states will become part of your nation when they are being attacked by another major, but the problem about that is when you vassalise some state that turns out to be so far away from other majors that that will pretty much never happen. Or they are completely surrounded by other minor regimes.
That's why I would also like some active way to integrate vassals into our nation. But it should be a longer process. Like, you would have to play this integration card multiple times, it would cost a lot of PP and it would also require very high relations.
3: Subordinate states feel incredibly lifeless right now. They don't seem to be doing anything, not moving their units at all and don't give you any events.
Normal minor regimes sometimes give events/decisions, which is nice, because it gives you some interaction between you and them, but once you turn them into subordinates, you don't ever hear anything from them again.
There should definitely be some events/decisions added for subordinate states.
4: Finally, here comes the biggest problem with subordinate states. We currently CANNOT move through their territory without declaring war.
That means, a new player might accidentally completely block themselves off from the rest of the world by vassalising too many minors.
There NEEDS to be a way for us to move our troops through client states without declaring war and we also need to be able to move logistics and supplies through their territory.