A page whose title is:
Dante's World Government:
De Monarchia in the 21st Century
By John J. Reilly
This is why Dante is heretic, if rightly resumed:
So, then, to take Dante's first question: Is the secular monarchy necessary?
Remarkably, Dante derives the necessity of monarchy from an argument that is almost Hegelian. Universal government is necessary, because it is the way to universal peace; universal peace is necessary, because it is the only way the human race can attain its end, or purpose; this end is actualization of the “possible intellect,” which is possessed by the human species as a whole.
The possible intellect got Dante into a lot of posthumous trouble; it was one of the reasons De Monarchia stayed on the Index of Forbidden Books from the 16th to the 19th centuries. The notion comes from the 12th-century Iberian Islamic philosopher, Averroes (Abu al-Walid Muhammad ibn Ahmad ibn Muhammad ibn Rushd), who deployed it in a way that argued against personal immortality in favor of a collective human soul. Dante himself thought no such thing, of course. His version rests on the scholastic commonplace that human beings are only partly intellectual beings (unlike angels, whose substance is intellect). Because of this defect, no single human being, however intelligent, could fully embody the intellectual capacity common to the species. That could be done only collectively and, since knowledge is cumulative, historically. The human species, if it is to achieve the state of intellectual perfection possible to it, required a peaceful and therefore unified world.
Be it noted that "possible intellect" has another meaning in St Thomas Aquinas, where it does not coincide with what he refutes while calling it "unity of intellect". See his work De Unitate Intellectus.
Be it also noted that these last lines:
Because of this defect, no single human being, however intelligent, could fully embody the intellectual capacity common to the species. That could be done only collectively and, since knowledge is cumulative, historically. The human species, if it is to achieve the state of intellectual perfection possible to it, required a peaceful and therefore unified world.
are true in a sense even a Moslem should have discovered non-applicable to this world here below: since that kind of peace and unity of all the righteous is what we truly (and they not without truth) apply to Paradise.
Here on earth, knowledge accumulates inequally, making individuals more knowing than their families' collective knowledge insofar as they lack time to fully share it, and families both more knowing and wiser than cities' or whole contries' shared knowledges and wisdoms.
Here is where Dante, but possibly (hopefully) not St Anselm, is wrong about soteriology:
Indeed, Christianity requires that the Roman Empire be legitimate. The central doctrine of Christianity is that Christ was punished for the sin of Adam. If the magistrate who sentenced Jesus was not an “appropriate judge,” then the suffering of Jesus was not a punishment, and we are not saved. Only the representative of the government of the whole world could have had the authority to inflict punishment on He Who suffered for the whole world.
And here is where Dante contradicts himself:
Inevitably in any medieval discussion of the temporal power of the papacy, Dante addresses the Donation of Constantine. This legend, aided by some forged documents, had it that, in the fourth century, the Emperor Constantine had given the pope the authority to govern Italy and the western empire. Dante does not dispute the authenticity of the Donation, but he says that nothing more could have been involved than the transfer of a right of guardianship.
Why so? Because, as Dante tells us, whatever is contrary to the nature of a thing is not to be numbered among its powers. Now one of the essential features of the empire is its universality; it has the right of universal jurisdiction, even when it does not have the fact. To divide the empire by ceding sovereignty over a particular region would have been to destroy the empire as such. The powers of the emperor, which derive from the nature of the empire, could not have included such a grant. Moreover, the Church by its nature could not have received such a grant, since the Church cannot own property, but only the fruits of property. (This was, of course, the ideal of the radical Franciscans.)
The tranquility of order that the emperor protects is important for the salvation of all men. The emperor's authority is therefore providential, but the authority belongs to the office itself. The authority of the emperor could not have come from the Church, since the empire antedates the Church. Furthermore, since the emperor's authority comes directly from God, the Electors of the Holy Roman Empire do not really choose the emperor. Rather, they simply declare where the right to the office lies.
In that case maybe Constantine simply declared that Roman authority resides in Sts Peter and Paul. With successors.
Be it also noted that these lines:
Moreover, the Church by its nature could not have received such a grant, since the Church cannot own property, but only the fruits of property. (This was, of course, the ideal of the radical Franciscans.)
are about not Franciscans as much as Fraticelli. Who were heretics.