I think they're similar to coalitions. Potentially awesome mechanics, that aren't quite there yet. Coalitions need to be more focused, and maybe even have a clear goal; and similarly PUs and succession wars need to be more tied into the idea of a balance of power.
I'd love to see something like the V2 crisis system whenever a succession war is going to break out. Rather than just have the two sides declare war, interested nations could back one or another side even if they don't have an alliance with one of the claimants.
I'd love to see something like the V2 crisis system whenever a succession war is going to break out. Rather than just have the two sides declare war, interested nations could back one or another side even if they don't have an alliance with one of the claimants.