It was therefore natural that St. Thomas Aquinas the greatest political writer of the Middle Ages should emphasize the necessity of unity in the political field, the harm of plurality of rulers, the dangers and damaging effects of demagogy.  The good of the state, says St. Thomas Aquinas, is unity.  And who can procure unity more fittingly than he who is himself one?  Moreover the government must follow, as far as possible, the course of nature and in nature power is always one.  In the physical body only one organ is dominant—­the heart; in the spirit only one faculty has sway—­reason.  Bees have one sole ruler; and the entire universe one sole sovereign—­God.  Experience shows that the countries, which are ruled by many, perish because of discord while those that are ruled over by one enjoy peace, justice, and plenty.  The States which are not ruled by one are troubled by dissensions, and toil unceasingly.  On the contrary the states which are ruled over by one king enjoy peace, thrive in justice and are gladdened by affluence.[2] The rule of the multitudes can not be sanctioned, for where the crowd rules it oppresses the rich as would a tyrant.[3]

Italy in the Middle Ages presented a curious phenomenon:  while in practice the authority of the state was being dissolved into a multiplicity of competing sovereignties, the theory of state unity and authority was kept alive in the minds of thinkers by the memories of the Roman Imperial tradition.  It was this memory that supported for centuries the fiction of the universal Roman Empire when in reality it existed no longer.  Dante’s De Monarchia deduced the theory of this empire conceived as the unity of a strong state.  “Quod potest fieri per unum melius est per unum fieri quam plura,” he says in the XIV chapter of the first book, and further on, considering the citizen as an instrument for the attainment of the ends of the state, he concludes that the individual must sacrifice himself for his country.  “Si pars debet se exponere pro salute totius, cum homo siti pars quaedam civitatis ... homo pro patria debet exponere se ipsum.” (lib.  II. 8).

The Roman tradition, which was one of practice but not of theories—­for Rome constructed the most solid state known to history with extraordinary statesmanship but with hardly any political writings—­influenced considerably the founder of modern political science, Nicolo Machiavelli, who was himself in truth not a creator of doctrines but a keen observer of human nature who derived from the study of history practical maxims of political import.  He freed the science of politics from the formalism of the scholastics and brought it close to concrete reality.  His writings, an inexhaustible mine of practical remarks and precious observations, reveal dominant in him the state idea, no longer abstract but in the full historical concreteness of the national unity of Italy.  Machiavelli therefore is not only the greatest of modern political writers,