The Hundred Years' War was a time of military evolution. Weapons, tactics, army structure, and the societal meaning of war all changed, partly in response to the demands of the war, partly through advancement in technology, and partly through lessons that warfare taught.
Before the Hundred Years' War, heavy cavalry was considered the most powerful unit in an army, but by the war's end, this belief had shifted. The heavy horse was increasingly negated by the use of the longbow (and, later, another long-distance weapon: firearms) and fixed defensive positions of men-at-arms — tactics which helped lead to English victories at Crécy and Agincourt. Learning from the Scots, the English began using lightly armoured mounted troops — later called dragoons — who would dismount in order to fight battles. By the end of the Hundred Years' War, this meant a fading of the expensively outfitted, highly trained heavy cavalry, and the eventual end of the armoured knight as a military force and the nobility as a political one.