Crusader Kings III - How to Take Down a Kingdom Quick

A cheeky method to seize a rival Kingdom in just two wars, with claims on just over 1/4 of its Counties.

Caveats

All credit goes to Sputnik !

This involves usurping titles. That works easily only against a Kingdom with a faith that’s non-hostile to your own. Usually there’s plenty of good targets nearby.
It assumes you have the means to win two wars against an enemy King – either through strength or guile. There’s other guides about all that business at the pointy end.
This method described here, although quick, is a little complex. Let me know in the comments of any missteps I’ve made and I’ll make amends.

Stuff You Need

Roughly in order of importance:

The ‘Chronicle Writing’ innovation
Gold in abundance
A good Chaplain

Chronicle Writing

This is an Early Medieval period Civic tradition. It takes a while to get, so set your culture ‘Fascination’ to this early (perhaps second only to Royal Prerogative)

Chronicle Writing opens two important war goals for us:

‘Your Claims’ lets you press any number of your own claims (rather than just one at a time)
‘Seize All De Jure Lands’ lets you war for any number of Duchies you have title to.

These are mutually exclusive goals in a single war. So that’s why we need to launch two wars.

Gold

“The sinews of war are infinite money” says Cicero. You won’t need that much!

But you will need enough gold to pay for all the titles you’ll be usurping and/or creating during the course of a 5 year truce period between wars (250 gold per Duchy and 500 for the Kingdom). But since you probably won’t have Chronicle Writing till your affluent mid-game this shouldn’t be a problem. (‘Ask Head of faith for Gold’ and ‘Extort Subjects’ are handy sources of extra cash).

Chaplain

A Chaplain with a high learning score will hasten the claims you still need to fabricate early on. But if you’re not your ‘Head of Faith’ you might be stuck with some idiot they gave you.

Take cheer – chaplains are quite easy to keep murdering until you get a good one.

Stuff to Do

As promised, your Chaplian need only fabricate claims for a little over 1/4 of the enemy Kingdom’s counties – but they have to be the right ones! Target half of the enemy Duchies plus one more. and fabricate claims on just over 50% of the counties within each (Shift+Q to see where the De Jure Duchies are on the map).
Declare war for all these by selecting the war goal ‘Your Claims.’ Be a winner.
During the 5 year end-of-war truce you’ve got some spending to do:
- ‘Usurp’ each Duchy you’ve just half-conquered Any duchy had no title to usurp you’ll have to create one for (either way, this will cost you 250 gold a pop).
- Now you’re holding titles over more than half of their Duchies you can do the same for their entire Kingdom. Usurp the Kingdom tile if it exists, or else create the title (500 more gold thanks)
After the truce period ends, declare a second war to Seize All De Jure Lands (Just check all the duchies you want are highlighted on the map before launch. If not, you may need to shake the money bag out again and grab those missing titles.
Win this second war to gain outright control of the emery’s kingdom. You know it’s right and proper.