My schoolbook history gave Simon de Montfort, 6th Earl of Leicester, credit for founding Parliament. Â English kings had been advised by a council of their principal tenants since before the Conquest, but de Montfort was the first - in 1262 to summon commoners to join the assembly.
Starting from that belief, it’s not hard to find irony in the fact that de Montfort’s father (also named Simon) was one of the military leaders of the crusade against the Albigenses, perhaps the first action in European history that deserves to be called genocide.
If this sort of historical irony displeases you, then you will be pleased, as I was, to find that the received story is not quite right. Â According to Hume’s History of England (Chap. XIII) , de Montfort did indeed summon representatives of the boroughs as part of his attempt to usurp the powers of Henry III, but that usurpation and de Montfort’s abuses of power left a bad taste in English mouths, and the idea of adding commoners to the Great Council was rather discredited than legitimized by its association with de Montfort’s scheme.
As Hume tells it, the origin of the Commons was the need of the monarchy for revenue. Â Henry’s son Edward I, finding himself in fiscal straits due both to structural changes unfavorable to the monarchy and to his aggressive campaigns in Wales, Scotland, and Poitou, found that his best source of new revenue were the boroughs, towns given a measure of local self-government under royal charter. Â While the king had the legal authority to tax the boroughs, he lacked the force to collect such taxes unless the burghers were more or less willing to pay them. Â Instead of negotiating the amounts borough-by-borough, he preferred to summon representatives of all the boroughs at once, lay out the sums he needed, and get them to agree as a group to supply his wants: Â “As,” he proclaimed, “it is a most equitable rule that what concerns all should be approved of by all, and common dangers be repelled by united efforts.” Â [Alas, the extant record does not include the critical press releases no doubt issued by Grover Norquist and the Club for Growth, explaining that Edward’s ideas would inevitably lead straight to Socialism.]
Edward’s innovation did not cause the House of Commons - combining the borough representatives with two knights from each shire - to spring into existence full-grown and fully armed.  Edward’s Parliaments did include the shire knights, in addition to the barons who had traditionally made up the Great Council and the newly-summoned burgesses.  But the burgesses plus the knights did not constitute a separate body from the House of Lords.  The barons and the knights deliberated jointly on matters of national concern, while the burgesses met only to approve their own taxation.  The legislative powers of the commoners accreted slowly, starting from the practice of  presenting petitions (“bills”) for redress of grievances as an implicit exchange for the supply of revenue.
On behalf of David Hume, I am happy to offer comfort to the .01% of you who were distressed about owing your political freedom in some measure to the son of a mass murderer, and to the possibly larger number who prefer structural to “great-man” explanations for important changes.
[Alas, the extant record does not include the critical press releases no doubt issued by Grover Norquist and the Club for Growth, explaining that Edward's ideas would inevitably lead straight to Socialism.]
To which Grover et al. would almost certainly respond: "Well, they did, didn't they?" Because, you see, 600 years is certainly a straight direction of time.
A Jesuit priest died and went to heaven. St. Peter escorted him to his accommodations. On the way there, they passed a beautiful palace with angels singing. The priest asked, "what's that St. Peter?". St. Peter said, "Oh, that's where the Dominican priests go when they die." Seeing the luxurious home for the Dominicans, the Jesuit began to be embarrassed by the expected opulence of the Jesuit's home in heaven — after all the Jesuits are the most prestigious order of priests in the entire church, much more so than the Dominicans.
St. Peter eventually stopped in front of an overgrown, dilapidated house. As a few bats flew out of the roof, St. Peter said, "Well, father, this is where the Jesuit priests go when they die." The Jesuit was aghast and confused, "Now, St. Peter, I am certainly glad to be here, but I couln't help but noticing on the way in that the Dominicans appear to have a slightly more agreeable situation. Not to take anything away from the Dominicans, but most people regard the Jesuits as the most pretigious order of priests in the entire church. What's the explanation for this?" St. Peter replied, "Well, father, I'm sure that you're aware that the Dominicans were formed to fight the Albigensian heresy, and the Jesuits were formed to fight the Protestants. And you've never heard of an Albigensian, have you?"
Without knowing enough to gainsay Hume, it bears minding that Hume's history is not a neutral document; Hume was a Tory, and would be ideologically disinclined to favor Montfort, a man whose capture and control of Henry III would've borne distinct echoes of the Charles I unpleasantness.
The textbook version in English school history is SFIK that de Montfort had the idea of the innovation, but that it was Edward who had the wisdom to see that his enemy's expedient served his own purposes, given his predilection for expensive and lengthy imperial wars, and so turned the innovation into an institution.
The historical question, it seems to me, is not how how parliaments started in England, since similar big-tent assemblies were a common feature of European feudal monarchies: but rather why the English one survived when the Spanish Cortes, the French Etats-Généraux, etc were swallowed up in absolutism.