This look back into the farther past shows a great deal about this Italian author, his choices, his assumptions, but he does this with only spare comments, and only now and then. The broad lines of what Guicciardini tells us in his narration comes down to us intact, and informed, with 220 years summed up clearly in just a few pages. Still the biases, as we may see them, from Guicciardini, nearly leap off the page.
Charles of Anjou first took and then was granted control of Naples, much of south Italy and Sicily in 1262 by his brother, French King Louis IX (St Louis) and the pope. This period was also fraught with much war and intrigue all over Europe, perhaps most spectacularly culminating in the Sicilian Vespers. This subject is probably best told in English in the book by that title, The Sicilian Vespers, by Steven Runciman.
The title of investiture granted to those ruling these lands became part of the legacy kept within the House of Anjou. Charles I of Anjou and Naples gave the title to his son, Charles II. When he died he gave it to his son Roberto, who had a son, Charles, called duke of Calabria. But this Charles died, and when Roberto grew old, he willed the Kingdom of the Two Sicilies, as these lands were then called, to his granddaughter, Joanna.
Queen Joanna ruled Naples for nearly forty years, was Countess of Provence, called princess of Achaea, Jerusalem and Sicily, and supported the French papacy at Avignon. At the age of seven in 1333, she was named Duchess of Calabria, and betrothed the next year, to her cousin Andrew who was also in the Hungarian line of House of Anjou. She may have loved him, but he didn't last long. Kept out of King Robert's will, he was set upon by different forces until he fell. Many years after his death and other captains, and husbands, having come and gone over the years, it was forces driven by a claim by the Hungarians who finally captured her and her husband, Otto. She had been careful, she had sought support and gained it from the French Kings of her time, John II and in turn Charles V, of the Valois line.
The wiki for Charles of Durrazzo, the man who would replace her, by act of pope Urban VI, has the effrontery to say that she was obsessed with him 'throughout her life'. But she had spent nearly the whole time in power - nearly fifty years - defending her lands in south Italy from the popes in Rome. A glowing picture of her court and reputation for advancing public health and granting benefices, her great personal piety and associations with notable contemporary mystics and saints like Catherine of Siena is to be found on wikipedia today. She was also Queen of Naples at the time that the bubonic plague struck Italy.
Guicciardini, has a very different view of this heir and her reign. He admits her lineage leading in a direct line back to the original Charles of Anjou and Naples, but says as little as possible about her.
"Giovanna for her Weakne∫se, and Di∫∫olute Cour∫e of Life, was very much de∫pi∫ed, and the de∫cendants of Charles the Fir∫t by Charles the Second (who left ∫everal children) endeavoured to dethrone her. The Queen, to procure A∫∫i∫tance, adopted for her Son Lewis Duke of Anjou brother to that King Charles, whom the French thought proper to di∫tingui∫h by the name Sage...". [book i, p. 36]Guicciardini gives neither source nor explanation for his claim here of 'Weakness', or a 'Dissolute Course of Life ' in this Joanna. Further he puts the actions for and against her coming from her own family as she was also descended from both Charles I and Charles II, like her cousins that Guicciardini lists by name only in a different context: Charles Durazzo. This Lewis above is that second Louis Duke of Anjou that came and tried to take Naples from Charles Durazzo after he ordered Joanna's assassination in 1382. This Charles Durazzo, once an ambassador in the wars between Venice and Croatia, was second cousin to Joanna in the same Anjou line from Charles II. He was the man picked by pope Urban VI to rule in Naples. And so he would remain, for a time. Joanna's body was brought back to Naples, shown in public and then thrown into a deep well at Santa Chiara Church, in Naples.
In quick succession after Charles Durazzo - after Louis III, the son of Louis (II) of Anjou mentioned above - came the heirs of Charles Durazzo, both Ladislav and Joanna, in turn. These became sovereign in Naples, carrying the familial and Angevin (House of Anjou) line into the fifteenth century. When Joanna II died in 1435, the line died with her as she had no children. It was this Joanna who had asked to procure Assistance from Alfonso V of Aragon which afterward, began the claims by that house on the Kingdom of Naples. She had left Naples to Rene of Anjou - the brother to Louis III - and it was Rene and Alfonso of Aragon who would spend the next decade fighting over the city's legacy. This Joanna is buried at Santa Annunziata, in Naples.
Guicciardini had little but harsh words for her as well. Rene of Anjou would bestow the unclaimed title of Naples to his son Charles, and he, to the French King Louis XI.
Quotes from The History of Italy, translated and printed by 1763 into English and found online at archive.org.