He who wishes to be obeyed must know how to command

... Whoever becomes master of a city accustomed to live in freedom and does no destroy it, may reckon on being destroyed by it. For if it should rebel, it can always screen itself under the name of liberty and its ancient laws, which no length of time, nor any benefit conferred will ever cause it to forget; and do what you will, and take what care you may, unless the inhabitants be scattered and dispersed, this name, and the old order of things, will never cease to be remembered...

The promise given was a necessity of the past: the word broken is a necessity of the present.

It is necessary for a prince wishing to hold his own to know how to do wrong, and to make use of it or not according to necessity.

Men ought either to be well treated or crushed, because they can avenge themselves of lighter injuries, of more serious ones they cannot; therefore the injury that is to be done to a man ought to be of such a kind that one does not stand in fear of revenge.

... From want of foresight men make changes which relishing well at first do not betray their hidden venom, as I have already observed respecting hectic fever. Nevertheless, the ruler is not truly wise who cannot discern evils before they develop themselves, and this is a faculty given to few.