All princes must build on strong foundations. The two essential components of a strong state are good laws and good armies. Good laws cannot exist without good armies. The presence of a good army, however, indicates the presence of good laws.
There are three types of armies: a prince’s own troops, mercenary troops, and auxiliary troops. Mercenary and auxiliary troops are useless and dangerous. Mercenaries are “disunited, undisciplined, ambitious, and faithless.” Because their only motivation is monetary, they are generally not effective in battle and have low morale. Mercenary commanders are either skilled or unskilled. Unskilled commanders are worthless, but skilled commanders cannot be trusted to suppress their own ambition. It is far more preferable for a prince to command his own army.
Historically, dependence on mercenaries ruined Italy. During the breakup of Italy, which the Church supported in hopes of increasing its own stature, many townships hired mercenaries because they had little experience in military matters. Since the mercenaries were more concerned with increasing their own prestige and status than with taking risks or accomplishing military objectives, the conflicts between these mercenary forces devolved into a series of ineffective, staged, pseudo-battles, ultimately degrading Italy’s political and military might.
Auxiliary troops—armies borrowed from a more powerful state—are as useless as mercenaries. Although they often fight well, a prince who calls on auxiliaries places himself in a no-win situation. If the auxiliaries fail, he is defenseless, whereas if the auxiliaries are successful, he still owes his victory to the power of another. Auxiliary troops are often skilled and organized, yet their first loyalty is to another ruler. Thus, they pose an even more dangerous threat to the prince than mercenaries.
If a prince does not command his own native troops, the principality can never be secure. Depending on outside armies is essentially the same as depending on good fortune. The use of auxiliaries and mercenaries is effective during prosperous times, but in times of adversity, reliance on borrowed troops, like reliance on fortune, is a perilous liability.
A prince must have no other objective, no other thought, nor take up any profession but that of war.
The only thing a prince needs to study is the art of war. This is the primary discipline of the ruler. Mastery of this discipline can make even a common citizen a great ruler. The easiest way to lose a state is by neglecting the art of war. The best way to win a state is to be skilled in the art of war.