I am playing as Arabia. Mali converted to Islam, I'm much bigger than him, he has every reason to vassalize, but he won't. In addition, he claims it is "out of his hands," although he isn't a vassal of anyone else. Some advice?
Do you already have the maximum number of vassals (4?)?
max (defensive pacts + vassals) = 6
I've had this problem lots of times. It's often caused by being at war with an indie or native civ when the would-be vassal isn't. I just go into the worldbuilder and change the diplomatic settings
How would being at war make him say, "It's out of our hands?"