I would focus on some of the changes associated with the conflict. One example might be the rise of nationalism, and really the nation-state, in both England and France. Another might be the changes in military technology and tactics. The use of longbows and gunpowder, for example, limited the effectiveness of heavy cavalry, which in turn helped to weaken the old feudal order, since men on horseback tended to be nobility. The conflict also caused, and witnessed major demographic change in France due to deaths from war, disease, and famine. The Hundred Years War coincided with the Black Death and a series of crop failures.