Would you care to provide any examples of this? It wouldn't happen to all be feudal states in western europe, which aren't really the same kind of thing as normal national borders at all?
Yes, I'll admit that a lot of the specifications I list to do with taking individual provinces are really mostly intended to apply to Europe. Because Europe has a lot of traditional political units that tended to change hands as whole pieces, and even when they were split apart, there was pressure to reunify them. The example I always go to for this is the empire of Matthias Corvinus. You can see that the territories he took exactly corresponded to Lusatia, Silesia, Moravia, Lower Austria, and Styria. And furthermore, after he died, the Bohemian lands he conquered basically automatically returned to Bohemia, because Matthias was only able to rule them by being a King of Bohemia. He couldn't integrate them into Hungary. But in the game there are no issues with this at all, if you repeat Matthias' conquests in the game, it just gets annexed into Hungary and Bohemia won't ever get it back unless they defeat Hungary in a war. You can just take random provinces from Bohemia and core them into Hungary. I am not exaggerating when I say that I think that any game that doesn't at least have some way of representing what is going on here is guaranteed to be bad, because it is inevitably going to produce nonsensical borders in Europe.
Even outside Europe, it seems to me that islamic empires often tended to just annex particular cities along with their hinterlands, and they weren't really drawing specific lines.
But like in general, I think we all agree that something has to be done to prevent stuff like this from happening. This for example isn't even based on regional elites enforcing traditional borders or anything, this just needs to stop happening. We should be thinking of ways to make it stop happening. That's what my post is about, even if I'm sort of struggling to talk about my points coherently.
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For another example, see the Russo-Turkish wars, where the Russian gains north of the Black Sea were always bordered by rivers, or for a few wars they just conquered Azov, an individual fortress. You could argue that this is because this region was basically just steppe, and in that case this should mean that in low-dev regions, borders are very usually based on either fortresses or natural borders like this. I think this needs to be represented in the game somehow. And maybe saying that you can only take in-game provinces in wars in certain contexts is the best way to do that.
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And like, perhaps you could make the argument that all of this should really be based on, like military defensibility or something (which kind of intersects with my argument that if you have no cooperation from local elites, your border would have to be determined purely by what you can control with forts). Like maybe we should try to think about making the war system function so that if you lose a battle in Egypt or Iraq, it's really easy for the winner to capture the rest of the area and difficult for the loser to keep control of it. But I'm not sure. I just know that this problem has to be solved somehow, or it will get even worse in Project Caesar than it is in eu4, because we have more locations that can be annexed individually in wars.