Having discussed the different types of states in Chapters 2 through 11, Machiavelli now turns to how to attack and defend them. Princes must lay good foundations, and those foundations include good laws and good armies. There cannot be good laws without good armies, and where there are good laws, there must be good arms, so Machiavelli declares he will only discuss arms, not laws.
Arms to defend the state are the prince's own, mercenaries, auxiliaries, or a mix of the three. Mercenaries and auxiliaries are dangerous and unreliable. If a mercenary is talented, he will always be trying to increase his power at the prince's expense. If he is incompetent, he will ruin the prince. Only princes and republics that can field their own armies can succeed, for mercenaries do nothing but lose. Those who are well armed can live free.
Machiavelli sites many examples of mercenaries who have turned on their employers. All this began when the Holy Roman Empire lost power in Italy and the popes gained power. Citizens took up arms against the nobles, and the popes encouraged them. Because neither the citizens nor the popes knew how to fight, they hired mercenaries. Soon mercenaries commanded every army in Italy. These mercenaries adopted strategies that kept them from hard work and danger, and this caused the ruin and humiliation of Italy.
