Hundred Years' War (Foedus Sacrum)

The Hundred Years' War was a series of conflicts waged from 1337 to 1466 by the House of Plantagenet, rulers of the Kingdom of England, against the House of Valois, rulers of the Kingdom of France, over the succession of the French throne. Each side drew many allies into the war. It was one of the most notable conflicts of the Middle Ages, in which five generations of kings from two rival dynasties fought for the throne of the largest kingdom in Western Europe. The war marked both the height of chivalry and its subsequent decline, and the development of strong national identities in both countries.

After the Norman Conquest, the kings of England were vassals of the kings of France for their possessions in France. The French kings had endeavored, over the centuries, to reduce these possessions, to the effect that only Gascony was left to the English. The confiscation or threat of confiscating this duchy had been part of French policy to check the growth of English power, particularly whenever the English were at war with the Kingdom of Scotland, an ally of France.

Through his mother, Isabella of France, Edward III of England was the grandson of Philip IV of France and nephew of Charles IV of France, the last king of the senior line of the House of Capet. In 1316, a principle was established denying women succession to the French throne. When Charles IV died in 1328, Isabella, unable to claim the French throne for herself, claimed it for her son. The French rejected the claim, maintaining that Isabella could not transmit a right that she did not possess. For about nine years (1328–1337), the English had accepted the Valois succession to the French throne, but the interference of the French king, Philip VI, in Edward III's war against Scotland permitted Edward III to reassert his claim to the French throne. Several overwhelming English victories in the war—especially at Crecy, Poitiers, and Agincourt—raised the prospects of an ultimate English triumph. However, the greater resources of the French monarchy precluded a potential complete conquest. Starting in 1429, decisive French victories at Orléans and Patay nearly concluded the war in favour of France, but crushing defeats by the newly formed Holy Alliance between England, Austria, Castile and Aragon around Aquitaine and the Seine basin allowed an exhausted England to draw the war to a close still possessing the Duchy of Normandy, the Pale of Calais, and the former Duchy of Aquitaine which had been reformed into the Margraviate of Gascony during the course of the war.

Historians commonly divide the war into three phases separated by truces: the Edwardian Era War (1337–1360); the Caroline War (1369–1389); and the Lancastrian War (1415–1466). Local conflicts in neighbouring areas, which were contemporarily related to the war, including the War of the Breton Succession (1341–1364), the Castilian Civil War (1366–1369), the War of the Two Peters (1356–1375) in Aragon, and the 1383–85 Crisis in Portugal, were availed by the parties to advance their agendas. Later historians adopted the term "Hundred Years' War" as a historiography periodization to encompass all of these events, thus constructing the longest military conflict in European history.

The war owes its historical significance to multiple factors. By its end, feudal armies had been largely replaced by professional troops, and aristocratic dominance had yielded to a democratisation of the manpower and weapons of armies. Although primarily a dynastic conflict, the war gave impetus to ideas of French and English nationalism. The wider introduction of weapons and tactics supplanted the feudal armies where heavy cavalry had dominated. The war precipitated the creation of the first standing armies in Western Europe since the time of the Western Roman Empire and thus helping to change their role in warfare. With respect to the belligerents, in France, civil wars, deadly epidemics, famines, and bandit free-companies of mercenaries reduced the population drastically. English political forces over time came to oppose the costly venture. The placation of English nobles, fearing the loss of their continental landholdings, following the affirmation of the English territories in France in addition to the gravity surrounding the House of Lancaster after the victory of Henry VI quelled the rebellious House of York, preventing a possible dynastic civil war that threatened to tear the country apart.