The Prince, by Machiavelli

My impression about this book was not correct. From what I heard, I gathered that this book is about arts of manipulation and deception, teaching princes how to yield obedience of their subjects using immoral means. This is not quite what the book is about.
Put simply, the book teaches princes, or princes want to be-s, how to acquire and retain princedom. The means to achieve that, as outlined in the book, can not all be considered ethical nor humane. However, this characterization does not apply to all the methods. It would seem that the author was outlining a practical guide focusing on attaining the result, not attempting to define the right way based on moral or religious basis. In that sense, it can be considered brutally correct.
Is there a benefit in reading this book? Not really sure. The book offers a historical perspective, and there is a question whether the methods presented therein still apply. I'd venture that yes, most do apply, and you can find evidences of their use by contemporary politicians and rulers. However, some of the methods are indeed dated, and others are clearly influenced by the political turmoil of Italy during the 1500s. I enjoyed reading the book as a historical account, more than a means of understanding how we are being governed these days.
I believe the most beneficial is a collection of quotes from the book. So, there you go:

"But when states are acquired in a country differing in language, customs, or laws, there are difficulties, and good fortune and great energy are needed to hold them, and one of the greatest and most real helps would be that he who has acquired them should go and reside there."

"The other and better course is to send colonies to one or two places, which may be as keys to that state, for it is necessary either to do this or else to keep there a great number of cavalry and infantry. A prince does not spend much on colonies, for with little or no expense he can send them out and keep them there, and he offends a minority only of the citizens from whom he takes lands and houses to give them to the new inhabitants; and those whom he offends, remaining poor and scattered, are never able to injure him; whilst the rest being uninjured are easily kept quiet, and at the same time are anxious not to err for fear it should happen to them as it has to those who have been despoiled."

"Upon this, one has to remark that 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."

".., for they knew that war is not to be avoided, but is only to be put off to the advantage of others, .."

"The wish to acquire is in truth very natural and common, and men always do so when they can, and for this they will be praised not blamed; but when they cannot do so, yet wish to do so by any means, then there is folly and blame."

"From this a general rule is drawn which never or rarely fails: that he who is the cause of another becoming powerful is ruined; because that predominancy has been brought about either by astuteness or else by force, and both are distrusted by him who has been raised to power."

"but, if once the Turk has been conquered, and routed in the field in such a way that he cannot replace his armies, there is nothing to fear but the family of this prince, and, this being exterminated, there remains no one to fear, the others having no credit with the people; and as the conqueror did not rely on them before his victory, so he ought not to fear them after it."

"Whenever those states which have been acquired as stated have been accustomed to live under their own laws and in freedom, there are three courses for those who wish to hold them: the first is to ruin them, the next is to reside there in person, the third is to permit them to live under their own laws, drawing a tribute, and establishing within it an oligarchy which will keep it friendly to you."

"But in republics there is more vitality, greater hatred, and more desire for vengeance, which will never permit them to allow the memory of their former liberty to rest; so that the safest way is to destroy them or to reside there."

"Nevertheless, he who has relied least on fortune is established the strongest."

"And in examining their actions and lives one cannot see that they owed anything to fortune beyond opportunity, which brought them the material to mould into the form which seemed best to them. Without that opportunity their powers of mind would have been extinguished, and without those powers the opportunity would have come in vain. "

"Because the innovator has for enemies all those who have done well under the old conditions, and lukewarm defenders in those who may do well under the new. This coolness arises partly from fear of the opponents, who have the laws on their side, and partly from the incredulity of men, who do not readily believe in new things until they have had a long experience of them."

"Hence it is that all armed prophets have conquered, and the unarmed ones have been destroyed."

"Therefore, he who considers it necessary to secure himself in his new principality, to win friends, to overcome either by force or fraud, to make himself beloved and feared by the people, to be followed and revered by the soldiers, to exterminate those who have power or reason to hurt him, to change the old order of things for new, to be severe and gracious, magnanimous and liberal, to destroy a disloyal soldiery and to create new, to maintain friendship with kings and princes in such a way that they must help him with zeal and offend with caution, cannot find a more lively example than the actions of this man."

"He who believes that new benefits will cause great personages to forget old injuries is deceived."

"Yet it cannot be called talent to slay fellow-citizens, to deceive friends, to be without faith, without mercy, without religion; such methods may gain empire, but not glory."

"Nevertheless, his barbarous cruelty and inhumanity with infinite wickedness do not permit him to be celebrated among the most excellent men."

"I believe that this follows from severities being badly or properly used. Those may be called properly used, if of evil it is possible to speak well, that are applied at one blow and are necessary to one's security, and that are not persisted in afterwards unless they can be turned to the advantage of the subjects."

"Hence it is to be remarked that, in seizing a state, the usurper ought to examine closely into all those injuries which it is necessary for him to inflict, and to do them all at one stroke so as not to have to repeat them daily; and thus by not unsettling men he will be able to reassure them, and win them to himself by benefits. He who does otherwise, either from timidity or evil advice, is always compelled to keep the knife in his hand; neither can he rely on his subjects, nor can they attach themselves to him, owing to their continued and repeated wrongs. For injuries ought to be done all at one time, so that, being tasted less, they offend less; benefits ought to be given little by little, so that the flavour of them may last longer."

"Because men, when they receive good from him of whom they were expecting evil, are bound more closely to their benefactor;"

"... and there will always be in doubtful times a scarcity of men whom he can trust. For such a prince cannot rely upon what he observes in quiet times, when citizens have need of the state, because then every one agrees with him; they all promise, and when death is far distant they all wish to die for him; but in troubled times, when the state has need of its citizens, then he finds but few. And so much the more is this experiment dangerous, inasmuch as it can only be tried once. Therefore a wise prince ought to adopt such a course that his citizens will always in every sort and kind of circumstance have need of the state and of him, and then he will always find them faithful."

"..., for men are always adverse to enterprises where difficulties can be seen, and it will be seen not to be an easy thing to attack one who has his town well fortified, and is not hated by his people."

"For it is the nature of men to be bound by the benefits they confer as much as by those they receive. Therefore, if everything is well considered, it will not be difficult for a wise prince to keep the minds of his citizens steadfast from first to last, when he does not fail to support and defend them."

"Mercenaries and auxiliaries are useless and dangerous; and if one holds his state based on these arms, he will stand neither firm nor safe; for they are disunited, ambitious, and without discipline, unfaithful, valiant before friends, cowardly before enemies; they have neither the fear of God nor fidelity to men, and destruction is deferred only so long as the attack is; for in peace one is robbed by them, and in war by the enemy."

"Auxiliaries, which are the other useless arm, are employed when a prince is called in with his forces to aid and defend, as was done by Pope Julius in the most recent times; for he, having, in the enterprise against Ferrara, had poor proof of his mercenaries, turned to auxiliaries, and stipulated with Ferdinand, King of Spain, for his assistance with men and arms. These arms may be useful and good in themselves, but for him who calls them in they are always disadvantageous; for losing, one is undone, and winning, one is their captive."

"And if it be urged that whoever is armed will act in the same way, whether mercenary or not, I reply that when arms have to be resorted to, either by a prince or a republic, then the prince ought to go in person and perform the duty of a captain; the republic has to send its citizens, and when one is sent who does not turn out satisfactorily, it ought to recall him, and when one is worthy, to hold him by the laws so that he does not leave the command."

"But the scanty wisdom of man, on entering into an affair which looks well at first, cannot discern the poison that is hidden in it, ..."

"I conclude, therefore, that no principality is secure without having its own forces;"

"A prince ought to have no other aim or thought, nor select anything else for his study, than war and its rules and discipline; for this is the sole art that belongs to him who rules, and it is of such force that it not only upholds those who are born princes, but it often enables men to rise from a private station to that rank."

"for a man who wishes to act entirely up to his professions of virtue soon meets with what destroys him among so much that is evil."

"Hence 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."

"Therefore it is wiser to have a reputation for meanness which brings reproach without hatred, than to be compelled through seeking a reputation for liberality to incur a name for rapacity which begets reproach with hatred."

"Therefore a prince, so long as he keeps his subjects united and loyal, ought not to mind the reproach of cruelty; because with a few examples he will be more merciful than those who, through too much mercy, allow disorders to arise, from which follow murders or robberies; for these are wont to injure the whole people, whilst those executions which originate with a prince offend the individual only."

"Upon this a question arises: whether it be better to be loved than feared or feared than loved? It may be answered that one should wish to be both, but, because it is difficult to unite them in one person, it is much safer to be feared than loved, when, of the two, either must be dispensed with."

"Returning to the question of being feared or loved, I come to the conclusion that, men loving according to their own will and fearing according to that of the prince, a wise prince should establish himself on that which is in his own control and not in that of others; he must endeavour only to avoid hatred, as is noted."

"Therefore, it is necessary to be a fox to discover the snares and a lion to terrify the wolves"

"Therefore a wise lord cannot, nor ought he to, keep faith when such observance may be turned against him, and when the reasons that caused him to pledge it exist no longer. If men were entirely good this precept would not hold, but because they are bad, and will not keep faith with you, you too are not bound to observe it with them."

"But it is necessary to know well how to disguise this characteristic, and to be a great pretender and dissembler; and men are so simple, and so subject to present necessities, that he who seeks to deceive will always find someone who will allow himself to be deceived."

"Therefore it is unnecessary for a prince to have all the good qualities I have enumerated, but it is very necessary to appear to have them. And I shall dare to say this also, that to have them and always to observe them is injurious, and that to appear to have them is useful; to appear merciful, faithful, humane, religious, upright, and to be so, but with a mind so framed that should you require not to be so, you may be able and know how to change to the opposite."

"From this one can draw another important conclusion, that princes ought to leave affairs of reproach to the management of others, and keep those of grace in their own hands."

"because I do not believe that factions can ever be of use; rather it is certain that when the enemy comes upon you in divided cities you are quickly lost, because the weakest party will always assist the outside forces and the other will not be able to resist."

"For this reason many consider that a wise prince, when he has the opportunity, ought with craft to foster some animosity against himself, so that, having crushed it, his renown may rise higher."

"And this question can be reasoned thus: the prince who has more to fear from the people than from foreigners ought to build fortresses, but he who has more to fear from foreigners than from the people ought to leave them alone."

"Nevertheless, not to extinguish our free will, I hold it to be true that Fortune is the arbiter of one-half of our actions, but that she still leaves us to direct the other half, or perhaps a little less."

"I conclude, therefore that, fortune being changeful and mankind steadfast in their ways, so long as the two are in agreement men are successful, but unsuccessful when they fall out. For my part I consider that it is better to be adventurous than cautious, because fortune is a woman, and if you wish to keep her under it is necessary to beat and ill-use her; and it is seen that she allows herself to be mastered by the adventurous rather than by those who go to work more coldly. She is, therefore, always, woman-like, a lover of young men, because they are less cautious, more violent, and with more audacity command her."

All quotes above are from a translation by W. K. Marriott, obtained via Project Gutenberg.