All the Habsburgs of OTL descend from Ernst I ‘der Eiserne’, Archduke of Austria and his second marriage to Cymburgis of Masovia (who passed the genes for what later became the Habsburg lip and prognathism into the family). However, Ernst had two older brothers (discounting the Albertine line) ahead of him in the succession who died without issue.

His eldest brother, Wilhelm, was married to the twenty-seven-year-old Giovanna II, Queen of Naples. They were married for five years with no children, and before marrying Giovanna he'd been a betrothed to Jadwiga of Anjou, Queen of Poland. His second brother, Leopold IV, married Catherine of Burgundy, but the marriage of nearly twenty-years left no issue. So naturally, Ernst succeeded to the Leopoldine line’s entire possessions.

So what if Wilhelm and/or Leopold IV had left kids (read: sons) to succeed to their titles – and in Wilhelm’s case, to their mother’s? How would this affect the Habsburgs development? Especially if the Ernestine line of the Leopoldines (at least the generation of Friedrich V (Holy Roman Emperor Friedrich III)) is still in existence. Would it mean that the Habsburgs could still climb onto the Imperial throne (assuming the Luxemburgs or the Albertine line are likewise unavailable as OTL)? Or at least be able to make themselves a pre-eminent family in Germany? Or would they be considered too foreign if they also rule the kingdom of Naples/Poland?
 
According to her wiki, Ernst married Cymburgis in Poland, after his brother's match with Jadwiga failed. Cymburgis was married off by her uncle, Jadwiga's husband, Jogaila/Wladyslaw II to strengthen ties with the Habsburgs. In the event of Wilhelm marrying Jadwiga, IDK know if the Ernst-Cymburgis match would even happen.

That said, we now have the house of Habsburg ruling Naples/Poland (Wilhelmine branch), their Austrian territories (Leopoldine branch), and then the Tyrolean branch. Now, I realize that the Polish throne wasn't hereditary, and quite possibly, if what I've read about Jadwiga jilting Wilhelm is true (that she refused him because he was German and the Poles didn't like Germans) she might lose the Polish throne. In such an event (her losing the Polish throne) who might they elect instead? And can she put a claim to the Hungarian throne after her sister, Maria dies without children? Or would that require a far earlier POD? And Poland is now sitting without a king, do they elect a Piast from one of the various branches floating around? The person with the next best claim after Lajos I's mother?
 
Alternately, if Wilhelm and Giovanna had managed to have issue (let's not go crazy, so I think at least one child, maybe two, at a stretch, would do it), how would this affect the history of the Neapolitan kingdom, and of Italy in general? @Yanez de Gomera, @LordKalvan and others could you help us out here? Would the Valois Angevins accept the Habsburg takeover any more than the Aragonese? Or would Giovanna's son be able to hold onto power because he's blood rather than an adopted heir?
 
@JonasResende

Polish throne was hereditary. It started to be elective in 1573 when last Jaggiellon (Zygmunt August) died without a heir. Szlachta would decide which house would rule their country only if there is no heir.
 
@JonasResende

Polish throne was hereditary. It started to be elective in 1573 when last Jaggiellon (Zygmunt August) died without a heir. Szlachta would decide which house would rule their country only if there is no heir.

My bad, I was under the impression that it was elective before the Jagiellons even got hold of the throne. (IDK where I read it but the szlachta also pressured Jadwiga not to marry Wilhelm and marry someone else instead). I could be wrong on both counts.
 
Well, let's imagine that Wilhelm dies as per otl in 1406, leaving let's say a hale and hearty son of one year or little more, wo Giovanna brings back to the Neapolitan Court. Let's also suppose that Ladislaus still catches the venereal disease that killed him in 1414 (unless you subscribe to the fancy theory of willful venereal poisoning).

It is likely that in 1412 it would be this son (named Leopold or Frederick I suppose) to be designated heir, and not Giovanna (who would stay as regent).
How would having a male heir influence Giovanna's character? Would she still take up Pandolfello Piscopo as favourite? How much her dissolute life is true, how much a slander againsta powerful woman?

It is possible that a boy king would be more easily recognized by pope John XXIII? Louis II of the main Anjou line will not voluntarily renounce his claim and a large part of the barons were on his part, a child king would not be that much of an upgrade in this respect. However it would probably mean that the Aragonese marriage is not pursued, instead it is possible that Giovanna might not marry (or secretly marry Pandolfello or Sergianni Caracciolo), or she might marry Muzio Attendolo Sforza, while an alliance is pursued by promising Wilhelm's son's hand to a suitable princess. But who might she be?

How could the Austrian lands be controlled from Naples? It seems impossible, maybe they could be ceded to Leopold IV or Enest in exchange for support for the coronation...

This is not an easy time to rule the Kingdom of Naples, it is a very difficult task for a woman and a child.
 
It is possible that a boy king would be more easily recognized by pope John XXIII? Louis II of the main Anjou line will not voluntarily renounce his claim and a large part of the barons were on his part, a child king would not be that much of an upgrade in this respect. However it would probably mean that the Aragonese marriage is not pursued, instead it is possible that Giovanna might not marry (or secretly marry Pandolfello or Sergianni Caracciolo), or she might marry Muzio Attendolo Sforza, while an alliance is pursued by promising Wilhelm's son's hand to a suitable princess. But who might she be?

How could the Austrian lands be controlled from Naples? It seems impossible, maybe they could be ceded to Leopold IV or Enest in exchange for support for the coronation...

This is not an easy time to rule the Kingdom of Naples, it is a very difficult task for a woman and a child.

I like Federigo, or, like the son and heir of Martin I of Sicily, he could be Federigo-Carlo, or something like that, couldn't he?

That said, I seem to recall reading somewhere that there was plan by Yolande of Aragon, duchesse d'Anjou to marry a daughter of hers (probably Marie, OTL queen of France) to the heir to the Aragonese/Barcelonid holder of Naples. Of course, for some reason the match foundered, and Marie married the dauphin and the Aragonese heir married a Castilian infanta. So would Marie be a suitable match here? Or would Giovanna need to play a sort of Elizabeth I game with her son, promising him everywhere to see who would be the most support?

And how if Giovanna/Federigo manages to hang on - if only by his bleeding fingernails - to the Neapolitan crown, would Habsburg possession of the throne be any different from Aragonese/Angevin rule OTL? And in what ways might it differ (if only superficially)?

As to the Austrian territories, I could see Leopold IV getting them. If how Ernst acted OTL with his relatives is anything to go by, it's a case of appointing him regent of those territories is like setting the fox to guard the hen-coop, so Giovanna would probably have to cede quite a bit in order to get them to come down on her side.
 
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