Answer:
According to Machiavelli, every prince must master the art of war, since war is the elemental form through which nations settle their questions of power. Therefore, if the prince masters the art of war, no one can dispute his power. It implies, therefore, that the prince dominate and monopolize the use of force and the way of applying it on those who seek to gain power over him.
Thus, every prince who seeks to maintain his power should know how to cause evil to those who challenge him, knowing how to administer this power so as not to incur unnecessary tyranny.