So I'm playing as Austria, it's going quite well. I've got most of the small German stats as my protectorates for just being stronger and a friendly guy I guess, but I had built up a big enough force that I decided it was time to go after Prussia, before they outdeveloped my technology.
So I beat them pretty badly, Took Berlin and West Prussia (they had 4 regions), but I kept searching the diplomatic menu and I could never find a force protectorate option.
Anyone else find a way to do this?