Not so invincible after all: Fastest declines of powerful dynasties and noble houses 1200-1500AD

The Union of the Crowns era Stuarts sort of implode over a relatively short period of time. They were only in-charge of England between 1603 and 1649 and 1660 to 1714 totaling 103 years and were incredibly unstable or actively at loggerheads with much of the leadership class for almost all of that time to the point that the second king of that union was executed by an assemblage of his own subjects for basically being crap at his job and failing to know when to settle for what he had. The direct line went into exile in 1688, never to be restored despite several attempts and eventually die out in 1807 and the secondary female line died out through a lack of heirs over the course of 26 years - only to be replaced by distant cousins because Parliament said so - whose female line descendents are still on the throne.

The Cromwell dynasty should also be counted, 1649-1660. Failed to create a viable alternative to the Stuarts, failed to settle any of the major issues in the state, failed to eliminate the concept of kingship and resorted to all but coping it for lack of a better option, fought what was to them godly civil wars that solved absolutely nothing and only made things much worse and ultimately unravelling over the course of about a year resulting into the restoration of their great enemies the Stuarts in 1660 with the support of one of their own henchmen George Monck, then richly rewarded with a Dukedom.

Much like the second half of the 15th century in England, the 17th century right across the Isles is just a dumpster fire from start to finish.
 
OP excluded "lack of male heirs" as reason of being sidelined
Well, there were male Angevins around, but Louis sidelined them in favour of his daughters, with ended badly for whole Capetian House of Anjou. Had Louis recognize Charles of Durazzo as heir, things would go better for dynasty.
 
Well, there were male Angevins around, but Louis sidelined them in favour of his daughters, with ended badly for whole Capetian House of Anjou. Had Louis recognize Charles of Durazzo as heir, things would go better for dynasty.

Maybe, but daughters of Louis still will be used probably by Luxembourgs or Bosnians to plot against Charles of Durazzo and they probably will have some support in northern Hungary (coincidentally the region from which most of Hungary's wealth was derived) judging by how there was short-lived uprising in name of Hedwig d'Anjou there when Mary died.
 
The Lascarid Empire. Looking really good on paper, poised to recover Constantinople before they themselves got ended in a coup and the state they built up suffering a rapid decline.

Yuan Dynasty and the Ilkhans also collapsed extremely rapidly.
 
Surprised no one mentioned the Staufer yet. By 1247 things looked not as stable as in earlier years, but under control, with a dead Heinrich Raspe, his successor as anti-king William of Holland looking fairly weak, a successful purge of Staufer opponents in southern Italy and the uprising in Parma looking to be containable. Friedrich II. had support from the majority of the German HRE princes, ruled Southern Italy, a daughter was married to the Byzantine emperor and he had a working relationship with the Abbayids and France. By 1250 he was dead, northern Italy in open rebellion, his successor unable to get the votes for emperor and forced out of Germany. By 1268 the last Staufer to rule anything lost to Charles of Anjou and was executed in Naples. At that point the dynasty was politically defunct: a few women married to various princes, a couple church positions, but mostly exiles and prisoners.
 
How much would you put their collapse as domestic problems vs. foreign ones?
With the HRE that is not a clear cut. In Northern Italy there was a long standing conflict how far the emperor ruled that part of the empire ans how independent it was.

Much of the trouble in Germany comes from the conflict with the Pope, which gave internal opponents a cause to rally against Staufer rule. How far can he be called an external actor for the HRE though, given the deeply interwoven structures? His Imperial allies also had sometimes other reasons to oppose the Staufer, not least the amount of resources the dynasty devoted to Italy.

Meanwhile in Southern Italy the main instigator for Charles of Anjou was again the pope, clearly both external actors. Otoh Anjou got the go ahead by the French King only after an internal conflict between Konradin and Manfred, the Staufer rulers in Southern Italy, which from his POV undermined Manfreds legitimacy to rule.

So I tend to more internal than external, but it is not clear cut. Than again how often is it ever clear cut, especially in medieval power structures?
 
I mean, not sure someone who'd been on the throne for ~2 years, had already faced one significant rebellion, and was widely regarded as a usurper counts as ''an invincible dynasty.''
He looked like he was invincible for a while, at least compared to Henry Tudor. Henry Tudor was just some guy with some French mercenaries who had been out of the country so long that he may as well as be seen as a foreigner. Henry Tudor’s claim was also extremely poor. Much poorer than Richard’s.
 
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