Full Idea
If a ruler acquires a state and is determined to keep it, he observes two cautions: he wipes out the family of their long-established princes; and he does not change either their laws or their taxes; in a short time they will unite with his old princedom.
Gist of Idea
To retain a conquered state, wipe out the ruling family, and preserve everything else
Source
Niccolo Machiavelli (The Prince [1513], Ch.3)
Book Reference
Machiavelli,Niccolo: 'The Prince, selections from Discourses', ed/tr. Plamenatz,J [Fontana 1972], p.61
A Reaction
This nicely illustrates the firmness of purpose for which Machiavelli has become a byword. The question is whether Machiavelli had enough empirical evidence to support this induction. The British in India seem to have been successful without it.