Hello everyone,
I would like to make a suggestion regarding territorial claims and casus belli.
As I understand, claims on sites that used to belong to you are already a thing. I think it would be interesting to expand this to regions. Giving any nation or nation level entity as well as individual nobles a claim to any region that they have at least one site in. Of course such claims would need to be enforced. This could happen through diplomacy, trying to make other entities agree to not build sites in your region using the same mechanic with which elves ask you to not harm trees. Maybe you could even convince them to hand over existing sites, by negotiation, bribes, threats or blackmail. Or, if diplomacy fails, through war. Such wars would then be limited to destroying or conquering foreign sites in the region and/or pushing out foreign armies from your claimed region.
This brings to my next idea: Casus belli (Latin for “occasion for war”). As things are right now, I think that wars are often way too destructive. Nations often end up being wiped out after losing 1 or 2 wars, or they just lose so many people that they never recover. In order to limit this, and make wars more interesting, I want to suggest the implementation of a system of war goals. Basically, the attacking nation provides a justification or states a goal for their war. And that justification then dictates what the attacker is aiming for, what actions are taken during the war, and under which conditions peace can be negotiated. Using the example of a territorial claim, the fighting would be (mostly but not necessarily entirely) limited to the region in question, as I described above.
A wide variety of casus belli could be added for such a system. Claims to regions, sites, even artifacts. Personal grievances between rulers. Economic or trade conflicts. Religious wars to spread a religion or fight someone over religious grievances for persecution in the past. Raids for slaves and loot. Wars to vassalize a nation or make them pay tribute. There are many possibilities. Using the new intrigue system, it might even be possible to fabricate claims or make a target nation provoke you, so that you can “rightfully defend yourself”. Also attacking without a casus bello should be possible but have consequences for the ruler who gave the order. Both external as well as internal.