Gavelkind post succession diplomatic adjustments

[Fitzjacob]

We've all been there. You hold five duchies have three sons, the first born is a count vassal to a different liege rotting away in a dungeon, the youngest is matrilineally betrothed to his non dynastic aunt and all of a sudden the Pope thinks it would be a good idea to...

Ahem, let me start over.

When your realm is divided between several heirs every single heir receives claims on each others titles. Since the AI always intends to press every claim they are never going to accept alliances due to "Political concerns" (-------).

Now usually one heir is slightly stronger than the others resulting in him declaring war on the weakest. Facing what is often 4 to 1 odds the weakest heir will still refuse alliances if offered by the middle heirs even as he stands on the brink of destruction. And the middle heirs can't use the "offer to join war" diplomatic action due to not fulfilling any requirement:

• You can offer to join the wars of allies.
• You can offer to join coreligionists in most religious wars and some rebellions.
• You can offer to join the war of a liege or above.
• You can offer to join certain vassal wars.

A player might want to maintain the status quo and always join the war on the side of the defending brother. They are prevented from doing so. And any AI controlled middle brothers will for some reason think that it's a great idea to also press their claims on the weakest brother even though they've won't have any chance to beat the original aggressor to the punch and can most certainly not stand up against him once he's got yet another duchy's worth of soldiers.

So I guess what I'm asking for is that after a realm has been split up by gavelkind the weaker successors contemplate pacts and gang up against the strongest if a conquering spree is initiated.

Add an additional opportunity to use the "offer to join war" action:

• You can offer to join close relatives in defensive wars.

And make the AI likely to choose that option if the aggressor has a claim on their titles as well.

Spoiler: Theories on bordergore

I believe it's actually the post succession behavior, rather than gavelkind itself, that is responsible for much of the bordergore in the game. Gavelkind does a pretty good job of ensuring that counties are inherited within their de jure duchies.

If a ruler owns six counties and three duchies and has three sons, then the sons will receive one duchy each and the counties that belong to their new duchy. This division is based on de jure laws with no concern to what's "fair" so one son may end up with four counties and the other two with one each.

However, after succession the strongest of them will usually retake his siblings duchies but the siblings will retain their counties within the duchies.

As gavelkind "strikes again" the ruler will now own three duchies but their demesne will only consist of counties within a single one of them. As the next generation heirs receive their duchies the game can't give all counties to a the single heir to whom they should belong since every heir must receive at least one county or they'd be landless. This causes the duchies to be divided up again with two of them having "stolen" land from the third.

Which is why we end up with stuff like this.

 

[Rags17]

Actually this would be a doddle for PDX to implement - simply give every heir under gavelkind an automatic Alliance with every other heir, with no timer or penalty for breaking the alliance. This means that initially at least a war of aggression would be near impossible if you had lots of siblings but over time the AI would let these free Alliances lapse and so they could be picked off piecemeal.