Parliament won the war, but the aristocrats lost the peace.
More radical supporters of Parliament's cause changed the course of the war and brought it to a conclusion unintended by those aristocratic Parliamentarians who originally challenged royal absolutism.
During the Stuart dynasty, a growing disenchantment with politics in the royal court led to the emergence of what historians have called a "country party" or faction. This "party" manifested a division that was both geographical and cultural. Its proponents emerged from the local politics of the English shires with little connection with the "court" politics surrounding the monarchy in London. They consisted of middle or lower gentry who participated chiefly in the local politics of their shire or county; a handful sat in the House of Commons. Moreover, they defined themselves culturally as distinctive from the court. The "court party," and all that is symbolized, became a negative reference group for this "country party." (In today's terms, the "court party" would be called "the political class.")
As historian Lawrence Stone summarized the way they viewed themselves,
"The Country was virtuous, the Court wicked; the Country was thrifty, the Court extravagant; the Country was honest, the Court corrupt; the Country was chaste and heterosexual, the Court was promiscuous and homosexual; the Country was sober, the Court drunken; the Country was nationalist, the Court xenophile; the Country was healthy, the Court diseased . . . the Country was the defender of old ways and old liberties, the Court the promoter of administrative novelties and new tyrannical practices; the Country was solidly Protestant, even Puritan, the Court was deeply tainted by Popish leanings."
These kind of people flocked into Parliament's New Model Army, led by Thomas Fairfax and Oliver Cromwell. This became a permanent professional army that replaced the traditional local militias. And these kind of people adopted a more radical solution to royal absolutism.
After the war, instead of simply modifying the monarchy and recognizing the supremacy of Parliament, the victors abolished the monarchy altogether. They put Charles on trial for treason and executed him. His son fled the country. Moreover, they completely restructured Parliament They abolished the House of Lords, that part of the constitution that most embodied the nobility and aristocracy. England declared itself a commonwealth--or republic. And the Presbyterian Church was established in place of the Church of England as the official church of the realm.
An aristocratic revolt against royal absolutism had turned into a middle class Puritan revolution.