DE MONARCHIA OF DANTE ALIGHIERI
CHAPTER V: When several things are ordained for one end, one must rule and the others obey.
1. Resuming what was said in the beginning, I repeat, there are three main questions asked and debated in regard to temporal Monarchy, which is more commonly termed the Empire, and it is my purpose to make inquiry concerning these in the order cited, according to the principle now enunciated. And so let the first question be whether temporal Monarchy is necessary for the well-being of the world. The necessity of temporal Monarchy can be gainsaid with no force of reason or authority, and can be proved by the most powerful and patent arguments, of which the first is taken on the testimony of the Philosopher in the Politics. There this venerable authority asserts that when several things are ordained for one end, one of them must regulate or rule, and the others submit to regulation or rule.  This, indeed, not only because of the author's glorious name, but because of inductive reasoning, demands credence. 
2. If we consider the individual man, we shall see that this applies to him, for, when all his faculties are ordered for his happiness, the intellectual faculty itself is regulator and ruler of all others; in no way else can man attain to happiness. If we consider the household, whose end is to teach its members to live rightly, there is need for one called the pater-familias, or for some one holding his place, to direct and govern, according to the Philosopher when he says, "Every household is ruled by its eldest."  It is for him, as Homer says, to guide and make laws for those dwelling with him. From this arises the proverbial curse, "May you have an equal in your house."  If we consider the village, whose aim is adequate protection of persons and property, there is again needed for governing the rest either one chosen for them by another, or one risen to preeminence from among themselves by their consent; otherwise, they not only obtain no mutual support, but sometimes the whole community is destroyed by many striving for first place. Again, if we consider the city, whose end is to insure comfort and sufficiency in life, there is need for undivided rule in rightly directed governments, and in those wrongly directed  as well; else the end of civil life is missed, and the city ceases to be what it was. Finally, if we consider the individual kingdom, whose end is that of the city with greater promise of tranquillity, there must be one king to direct and govern. If not, not only the inhabitants of the kingdom fail of their end, bit the kingdom lapses into ruin, in agreement with that word of infallible truth, "Every kingdom divided against itself is brought to desolation."  If, then, this is true of these instances, and of all things ordained for a single end,  it is true of the statement assumed above.
3. We are now agreed that the whole human race is ordered for one end, as already shown. It is meet, therefore, that the leader and lord be one, and that he be called Monarch, or Emperor. Thus it becomes obvious that for the well-being of the world there is needed a Monarchy, or Empire.
1. Pol. 1. 5. 3: "Whatsoever is composed of many parts, which together make up one whole, ... shows the marks of some one thing governing and another thing governed."
Conv. 4. 4. 2: "And with these reasons we may compare the words of the Philosopher, when he says in the Politics that when many things are ordained for one purpose, one of them should be governor or ruler, and all others should be governed or ruled."
2. For Dante's idea of the deference due to authority, philosophical and imperial, see Conv. 4. 8. 9.
3. Pol. 1. 2. 6.
4. Homer, Od. 9. 114, quoted by Arist. Pol. 1. 2. 6.
5. "Politia obliqua."
6. Luke 11. 17.
7. Conv. 4. 4. 2: " Even as we see a ship, where her divers duties and their divers purposes are ordained for one end, that is, to bring her by a safe course to the desired haven, where, as each officer performs his own duty with regard to the proper end, so there is one person who considers all these, and adapts them all to the final end, and this one is the pilot whose voice all must obey. And this we see in religious bodies, and in armies, and in all things, which, as we have said, are ordained for some one purpose."