The doctrine of "reason of state" is a slippery concept to define, having been used by many writers with different shades of meaning. In general, it refers to the idea that the well-being and stability of the state is paramount, and all of the government's actions should be directed to this end. This includes actions which would be considered illegal or immoral under ordinary circumstances. Machiavelli did not invent this doctrine, which can be found in the writings of many Classical authors, most notably, Tacitus. Machiavelli probably derived it from his study of Livy, Xenophon, and Aristotle. In fact, Machiavelli does not use the phrase "reason of state," which was first popularized by fellow Italian Giovanni Botero in his 1589 book, Ragione de Stato. Nonetheless, Botero's book draws heavily on Machiavelli's ideas, and Machiavelli is usually credited as the first modern writer to systematically describe the principles of reason of state.
Implicit throughout The Prince is the notion that almost any action of a ruler is justifiable if it contributes to the peace, prosperity, and stability of the state. Machiavelli endorses murder, deceit, violence, and cruelty, provided they are directed toward the greater good. He applauds Cesare Borgia's cruelty in subduing the Romagna because it ultimately brought peace and safety to the previously lawless region. In Machiavelli's defense, he does not endorse deceit or violence for its own sake. He assumes that there is a basic level of violence and injury that rulers cannot avoid. The key is to make the best use of this unavoidable cruelty. Actions that injure a few are better than actions that injure many. This principle can be seen in his discussion of colonies as a means of subduing a newly conquered territory. Colonies deprive a few people of their lands and homes, but they are preferable to occupation by an army, which injures and offends everyone in the territory. The greater good is clearly a consideration here. However, Machiavelli also makes clear his other primary consideration: The people who are injured by colonies are too few, too poor, and too scattered to pose any threat to the ruler who abuses them, while entire populations that hate and despise the new ruler are a definite threat to that ruler's continued power.
Botero accused Machiavelli of having a reason of state based on lack of conscience. Whether you accept Botero's judgment or not, he has pointed out the central problem with the concept: It is extremely difficult to separate reason of state from pure self-interest, and the questionable actions that promote the health of the state from those that promote the personal ambitions of the ruler. Because of this, reason of state has become associated with tyranny, and Machiavelli's brand in particular has been seen as a justification of absolutism and authoritarianism. Some critics have tried to defend Machiavelli by pointing out that The Prince is not a discourse on morality, but a purely technical, analytical study of political power. For this reason, Machiavelli is often described as the first true political scientist, someone who presented an impartial observation of politics as they truly are, rather than as theory dictated they should be. In doing so, he can be seen in the same light as Renaissance scientists like Galileo, who discarded traditional explanations of phenomena which were not consistent with their empirical observations of the workings of nature. In The Prince, the concept of the state has become autonomous and self-contained. Divorced from traditional Western concepts of Christian morality, it becomes an end unto itself, carrying along its own independent standard of behavior.
Reason of state fell out of fashion as a political philosophy by the end of the 17th century, but reappeared in the mid-19th century as realpolitik, a term often applied to the policies of German chancellor Otto von Bismarck. The dictionary defines realpolitik as "foreign policy determined by expediency rather than ethics or world opinion; power politics." The term is often translated as "practical politics," or politics that accomplish the goals of the state in the real world, rather than a world based on theory or idealism. One of the assumptions of realpolitik (or political Realism) is that all states act to maximize, or at least to preserve, their own power. Therefore, all international relations are based on a struggle for power. The opposing concept is Idealism, which assumes that different states have a basic harmony of interests. It is easy to see Machiavelli's influence on Realism, remembering his insistence that he would discuss things as they really are, as well as his strategic analysis of the best ways to acquire and keep power.