Final answer:
One of the causes of the Hundred Years' War was the dispute between England and France over claims to French lands. The use of new weapons and tactics during the war also diminished the role of noble knights in warfare. The growth of professional armies provided social mobility for peasants.
Step-by-step explanation:
One of the causes of the Hundred Years' War was the conflict between England and France over claims to French lands held by the English monarch. The tension escalated when King Charles IV of France died without a son, and the crown was given to his nephew Philip. However, King Edward III of England maintained that he had a greater right to the throne of France. This dispute led to widespread political factionalism and devastation, especially in France where most of the fighting took place.
The Hundred Years' War also brought about changes in warfare and decreased the importance of the noble knights. The use of new weapons and tactics, such as the longbow, by large professional standing armies financed by monarchs, made the feudal cavalry-focused armies obsolete. This shift in warfare chipped away at the traditional feudal privileges and prestige of the social elites.
The growth of professional armies during the Hundred Years' War also offered peasants the opportunity for social mobility, as they could earn a regular wage for military service.