Would it be possible for the rebellion led by Simon De Montfort to result in either a severely limited monarchy (with the king as a mere figurehead) or an outright Republic?
A republic in the 13th century is not possible in England.
In the 13C if a baron were powerful enough to reduce the king to such a condition, he would be powerful enough to depose the king and seize the throne for himself.
Why would nobles create a republic?
In the 13C if a baron were powerful enough to reduce the king to such a condition, he would be powerful enough to depose the king and seize the throne for himself.
Why would nobles create a republic?
I suppose King John was hated enough to where the Barons, had they felt sure eonough of themselves, could have deposed John and established an elected monarchy similar to the Holy Roman Empire. IE. Parliament (the House of Lords) elects the King from one of their number whenever the King dies similar to the Holy Roman Empire. Or an English King could attempt to bring England into the HRE.
Or for that matter, Charlemange could have conqured the British Isles INTO the Holy Roman Empire if at some point he decided to march west before he marched east to the Oder. Saxon England was relatively weak in the 800s and could likely not have stood against Charlemange. Nor likely could Wales, Scotland or Ireland. The British Isles could wind p in the HRE via the Low Countries after Charlemange's death rather than part of France.
A republic in the 13th century is not possible in England...
Yes. Urban republics, little city-states that in the XIII century were territorialy as much important than a township. Socially, they were at best the result of alliance between local nobility (aristocratic or milites) and urban elites : however, it was more for southern Europe where north european communes were usually exempt of aristocratic social support.Its not as though there were no republics at the time.
And for someone like no real dynastic claim, such as Simon de Montfort, to achieve a position of influence. Republic need not mean democracy, and the Second Barons' War certainly seemed to be headed in the direction of a figurehead king if not a republic outright, if the Barons had won.
Saying nothing about the most important question : why?Did Charlemange have truly blue water capable ships available? Otherwise what you are suggesting would take far more time than Charlemagne would have to live. Consider the problems of trying to fight in the harsh terrain of Northern Saxon England, Scotland, Wales, and in terms of LOCs, Ireland.
IOTL he married one of King Henry's sisters, so his children would have had a dynastic claim albeit not the strongest one...And for someone like no real dynastic claim, such as Simon de Montfort, to achieve a position of influence.
That problem could easily be solved by killing Edward I. It would not be outside the realm of possibility for Edward to die in one of the battles during the war, perhaps if Eversham somehow went the other way Edward might die along with many other royalist leaders while Henry III himself remains a captive of de Montfort's.A republic in the 13th century is not possible in England. Making the King a figurehead with actual power in the hands of a Baronial Council is certainly feasible with a weak king like Henry III, but not as a permanent constitutional change. OTL Edward I would certainly have not abided by such control and would challenge it immediately. And he certainly would have found supporters among the nobility leading to another civil war. However, if ITTL Henry's successor is an easily controled weakling like OTL Edward II it could make Baronial control seem permanent. But still an illusion short of an elective monarchy or some way to ensure that only sots and imbeciles sit on the throne. Any capable and strong-willed monarch will find a way to assert himself and reestablish Monarchial rule.