The work depicts a debate between the king himself, his illegitimate son Prince János (John Corvinus), and Florentine knight and merchant Domenico Giugni.
In framing Republics and Kingdoms Compared as a Socratic argument, Brandolini breaks from the Italian humanist tradition of employing Ciceronian dialogues to examine political theory.
Three days before Lent, Prince János states to his father that his classical studies have led him to suppose that modern rulers are more decadent than their ancient counterparts.
[3] Matthias Corvinus informs his son János that rulers both ancient and modern must adopt two domestic and two external virtues to maintain their political regimes.
[5] Matthias' claim prompts János to ask whether republics or kingdoms are more suited to promoting liberty, justice, and good governance.
János then beckons Domenico Giugni, a merchant in Matthias' entourage with political and socioeconomic ties to the Republic of Florence, to join the conversation.
While answering Matthias' probing questions, Domenico states that Florentine liberty is grounded on the ability to impose taxes without free from the influence of foreign powers.
Book I ends with Prince János' summation that the Florentine Republic "is not free but is in servitude to itself," and that "no one ever can enjoy solid peace and tranquility so long as he wants to be a good citizen.
Domenico admits that Florence's laws were instituted by individual citizens, leading Matthias to conclude that legislation is the responsibility of kings.
[17] He claims that commerce caused the destruction of the Athenian democracy and the Roman Republic, but admits that trade divorced from greed is admirable and healthy for political regimes.
[18] Matthias condemns modern republics like Florence that utilize commercial relations to divide citizens by economic status, and for allowing this division to stymie the equal implementation of the laws.
[25] Matthias believes kingdoms, where one man surpasses all others in virtue and ambition, provide a more likely avenue for promoting good governance than republics.
Matthias then reminds Dominicio that the Christian religion, administered by a single omniscient and omnipotent God, is the model all political regimes should strive to emulate.
[28][29] Professor Allison K. Frazier of the University of Texas at Austin connects Brandolini's decision to frame his work as a Socratic dialogue with the Latin translations of Plato's Statesmen and Laws by Marsilio Ficino which had been recently published and had begun circulating within the Hungarian court.
Frazier also remarks on the curious circumstances that led Brandolini, a Florentine humanist, to support monarchy so prominently in his treatise.
[30] Critic Raffaele Florio proposes that Brandolini's Republics and Kingdoms Compared be read as a companion to Machiavelli's Discourse on Livy and The Prince.
He also recognizes Brandolini's treatise as a unique snapshot "of the late fifteenth-century Florentine Zeitgeist, and suggests that lecturers and professors use it to freshen up the traditional political theorist lineup of Aristotle, Thomas Hobbes, John Locke, and Jean-Jacques Rousseau.
Writing under the pseudonym Quintus Curtius, Thomas proposes that, like Machiavelli, "Brandolini looked hopefully to a strong, centralized government as an antidote to the fratricidal wars of the Italian micro-republics.