Dante Alighieri & Pope Benedict XVI on the necessity for Universal Political Authority

De Monarchia (I, xiv, 1-11)
(1) And what can be brought about by a single agent is better done by a single agent than by more than one. This can be explained as follows: let there be one agent (A) by which something can be brought about, and let there be several agents (A and B) by which it can equally be brought about; now if that same thing which can be brought about by means of A and B can be brought about by A alone, then B is introduced unnecessarily, because nothing is achieved by the introduction of B, since that same thing was already achieved by means of A alone.
(2) And since the introduction of any such means is unnecessary and pointless, and everything which is pointless is displeasing to God and to nature, and everything which is displeasing to God and to nature is evil (as is self-evident), it follows that not only is it better that something should be brought about by a single agent, where that is possible, rather than by several, but that being brought about by a single agent is good, by more than one is in absolute terms bad.
(3) Moreover, a thing is said to be better the closer it is to the best; and the goal itself is the measure of what is best; but to be brought about by a single agent is closer to the goal; therefore it is better. And that it is closer can be shown as follows: let the goal be C; let the achieving of that goal by a single agent be A, and by several agents be A and B; it is clear that to go from A through B to C is a longer route than to go from A directly to C.
(4) But mankind can be ruled by one supreme ruler, who is the monarch. On this point it must of course be noted that when we say "mankind can be ruled by one supreme ruler", this is not to be taken to mean that trivial decisions in every locality can be made directly by him - even though it can happen that local laws are sometimes defective and there may be a need for guidance in implementing them, as is clear from what Aristotle says in the fifth book of the Ethics when he commends the principle of equity.
(5) For nations, kingdoms and cities have characteristics of their own, which need to be governed by different laws; for law is a rule which governs life.
(6) Thus the Scythians, who live beyond the seventh zone and are exposed to nights and days of very unequal length, and who endure an almost unbearable intensity of cold, need to have one set of laws, while the Garamantes require different laws, since they live in the equatorial zone and always have days and nights of equal length, and because of the excessive heat of the air cannot bear to cover themselves with clothes.
(7) It is rather to be understood in this sense, that mankind is to be ruled by him in those matters which are common to all men and of relevance to all, and is to be guided towards peace by a common law. This rule or law should be received from him by individual rulers, just as the practical intellect, in order to proceed to action, receives the major premiss from the theoretical intellect, and then derives the minor premiss appropriate to its own particular case, and then proceeds to the action in question.
(8) And it is not only possible for one person to do this, but necessary for this to come from one person, to avoid any confusion about universal principles.
(9) Moses himself writes in the Law that he did just this when, having chosen certain leaders from the tribes of the sons of Israel, he left less important judgments to them, retaining for himself alone the more important ones which concerned all of them; these judgments of more general relevance were then applied by the leaders to their tribes, according to what was appropriate for each particular tribe.
(10) Therefore it is better for mankind to be ruled by one person than by several, and thus by a monarch who is the only ruler; and if this is better, then it is more acceptable to God, since God always wills what is better. And since when there are only two things being compared, the better is the best, it follows that when the choice is between "one" and "more than one", not only is the first of these more acceptable to God, but it is entirely acceptable.
(11) It follows from this that mankind is in its ideal state when it is ruled by one person; and thus monarchy is necessary to the well-being of the world.

Pope Benedict XVI CARITAS IN VERITATE
67. 'In the face of the unrelenting growth of global interdependence, there is a strongly felt need, even in the midst of a global recession, for a reform of the United Nations Organization, and likewise of economic institutions and international finance, so that the concept of the family of nations can acquire real teeth. One also senses the urgent need to find innovative ways of implementing the principle of the responsibility to protect and of giving poorer nations an effective voice in shared decision-making. This seems necessary in order to arrive at a political, juridical and economic order which can increase and give direction to international cooperation for the development of all peoples in solidarity. To manage the global economy; to revive economies hit by the crisis; to avoid any deterioration of the present crisis and the greater imbalances that would result; to bring about integral and timely disarmament, food security and peace; to guarantee the protection of the environment and to regulate migration: for all this, there is urgent need of a true world political authority, as my predecessor Blessed John XXIII indicated some years ago. Such an authority would need to be regulated by law, to observe consistently the principles of subsidiarity and solidarity, to seek to establish the common good, and to make a commitment to securing authentic integral human development inspired by the values of charity in truth. Furthermore, such an authority would need to be universally recognized and to be vested with the effective power to ensure security for all, regard for justice, and respect for rights. Obviously it would have to have the authority to ensure compliance with its decisions from all parties, and also with the coordinated measures adopted in various international forums. Without this, despite the great progress accomplished in various sectors, international law would risk being conditioned by the balance of power among the strongest nations. The integral development of peoples and international cooperation require the establishment of a greater degree of international ordering, marked by subsidiarity, for the management of globalization. They also require the construction of a social order that at last conforms to the moral order, to the interconnection between moral and social spheres, and to the link between politics and the economic and civil spheres, as envisaged by the Charter of the United Nations.' Benedict XVI