Unfortunately the word mediatise isn't anything to do with either the media or promulgating things. It means to annex another state while allowing its former ruler to retain his title and some degree of authority.
This is yet another reason why I'd be jolly glad if the wretched word just bit the flipping dust.
Word Not To Use Today: mediatise. This word comes from the French médiatiser, from the Latin mediāre, to be in the middle.