So, right now I'm the king of Burgundy. I started with the Duchy of Upper Burgundy ruled by the Welfs. So after about 30-40 years I'm the King. It was pretty hard, because of the Karling dynasty, but Plotting proved useful.
So my question now is, how do I spread my dynasty, the Welfs to other duchies and Kingdoms ? Through matrilineal marriage ? In my last campaign I had one other duchy ruled, by a member of my dynasty, but I can't remember how I did that.