Its basic cause was a dynastic quarrel that originated when the conquest of England by William of Normandy created a state lying on both sides of the English Channel. In the 14th cent. the English kings held the duchy of Guienne in France; they resented paying homage to the French kings, and they feared the increasing control exerted by the French crown over its great feudal vassals. The immediate causes of the Hundred Years War were the dissatisfaction of Edward III of England with the nonfulfillment by Philip VI of France of his pledges to restore a part of Guienne taken by Charles IV; the English attempts to control Flanders, an important market for English wool and a source of cloth; and Philip's support of Scotland against England.

The war may be dated from 1337, when Edward III of England assumed the title of king of France, a title held by Philip VI. Edward first invaded France from the Low Countries (1339–40), winning small success on land but defeating (1340) a French fleet at the battle of Sluis. In 1346 he won the battle of Crécy and besieged Calais, which surrendered in 1347. In 1356 the English won the battle of Poitiers, capturing King John II of France. After prolonged negotiations, the Treaty of Brétigny was signed (1360); England received Calais and practically all of Aquitaine, as well as a large ransom for the captive king.

The Gascon nobles, oppressively taxed by Edward the Black Prince, appealed (1369) to King Charles V. The war was renewed, and by 1373, Du Guesclin had won back most of the lost French territory. In 1415, Henry V of England renewed the English claims, took Harfleur, and defeated France's best knights at Agincourt. By 1419 he had subdued Normandy, with the connivance of John the Fearless, duke of Burgundy. Philip the Good, successor of John the Fearless, mediated between Henry V and Charles VI of France (see Troyes, Treaty of), and Charles recognized Henry as heir to the crown of France.

By 1429 the English and their Burgundian allies were masters of practically all France N of the Loire, but in that year Joan of Arc raised the siege of Orléans and saw Charles VII crowned king of France at Reims. Her capture by the Burgundians and her judicial murder after extradition to the British did not stop the renewal of French successes. In 1435, Charles obtained the alliance of Burgundy (see Arras, Treaty of). By 1450 the French reconquered Normandy, and by 1451 all Guienne but Bordeaux was taken. After the fall (1453) of Bordeaux, England retained only Calais, which was not conquered by France until 1558. England, torn by the Wars of the Roses, made no further attempt to conquer France.

The Hundred Years War inflicted untold misery on France. Farmlands were laid waste, the population was decimated by war, famine, and the Black Death (see plague), and marauders terrorized the countryside. Civil wars (see Jacquerie; Cabochiens; Armagnacs and Burgundians) and local wars (see Breton Succession, War of the) increased the destruction and the social disintegration. Yet the successor of Charles VII, Louis XI, benefited from these evils. The virtual destruction of the feudal nobility enabled him to unite France more solidly under the royal authority and to promote and ally with the middle class. From the ruins of the war an entirely new France emerged. For England, the results of the war were equally decisive; it ceased to be a continental power and increasingly sought expansion as a naval power.