Download Diplomatic Options - Vassal, Liberate & Confederate

This mod allows all factions to vassalize, liberate and confederate other factions. Confederation can be done with any other faction of the same type, however different culture types cannot confederate. All factions can liberate other factions, but keep cultural relations in mind or you'll have a new declaration of war on your hands. Finally, you can vassalize other factions either through conquest or diplomacy, however the latter requires a new game.

Credits: Dresden