Detachment and decisiveness.
In this excerpt Machiavelli counsels the prince to be prepared to go all the way and destroy a conquered city or kingdom or in turn, 'be destroyed by it'.
He points out that the citizens of a political entity, city or kingdom who have enjoyed the benefits of liberty or freedom under the previous ruler or government, unless decimated, dispersed or destroyed, will rise against their new conqueror when summoned to it by anyone using liberty as its calling banner. He gives the adequate example of Florence to drive the point home