The major cause of the war was the quarrel between dynasties of England and France: the King of England, Edward III was dissatisfied with the policy of Philip VI, the King of France, with regard to the region of Aquitaine, and wanted to return control over this region to England (Hansen & Curtis, 2008). Then, there also was an economic conflict, as French king wanted to increase taxes for Flanders towns, which evolved into large cloth-making and trade centers. These towns, in their turn, sought help from England and asked Edward III for support. Philip VI also supported Scotland in its struggle against England (Hansen & Curtis, 2008), which also added to the causes of the war.
The Hundred Years War was in fact not a single war, but a series of wars followed by short periods of peace. Continued conflicts took place mainly because of power disposition: the King of England was in fact the vassal of the King of France, but ruled more French territories than the Kind of France. In the end of the series of three wars – the conquest of Normandy, the Saintonge War and War of Saint-Sarbos (Hansen & Curtis, 2008) – the English were pushed out of the continent and only possessed small provinces in Gascony. In these wars, the success was variable: in 1340, the English gained control over the channel close to Dunkerque, defeated the French at Crecy, and occupied Calais; however, in the 1380s the success passed to the French (Hansen & Curtis, 2008). Finally in 1429 the French have united, due to the feat of Joan of Arc; the French besieged the English and pushed them back to the islands, everywhere, except Calais (Hansen & Curtis, 2008).
This war resulted in the rise of nationalism for both countries, and greatly contributed to military development of both English and France. New technologies emerged during these wars, e.g. gunpowder. However, the war also exhausted resources of both countries, and a period of misery, famine and Black Death unfolded in France. At the same time, the next French King, Louis XI, managed to unite France because of this depressive period, and established strong royal authority. England ceased the power on the continent, and turned to gaining larger naval power. Consolidation of power took place in both monarchies (Hansen & Curtis, 2008), and in England, Parliament was created.
Hansen, V. & Curtis, K.R. (2008). Voyages in World History. Cengage Learning.