In Chapter 5 “Concerning the way to govern cities or principalities which lived under their own laws before they were annexed” of The Prince by Niccolò Machiavelli it is stressed how the Prince should deal and conquer self-governing places as democracies or republics.
He says that no democracy or republic would like to be governed or controlled by a king, that they also would not support a king, they would rather stay free so he suggested the Prince should just burn them out or destroy them.