Hoi4: Bourbon France unites with Carlist Spain on historical

In this video I'm trying out something Hatless Spider already did. It took me five tries to get it done, it really is harder than it looks.
The challenge was, playing as France, to get the Kingdoms of France and Spain to unite, on historical. The tricky part is that on historical, the Carlist faction usually doesn't spawn, let alone win.

The Hatless Spider video:
https://youtu.be/ngRfxy1anWo

Soundtrack, once again, from the Age of Wonders game