The lengthy conflict between England and France and their various allies, now known as the Hundred Years War, broke out after the death of Charles IV of France without a male heir. Charles' closest male relative was his nephew, the English King Edward III, who also controlled extensive lands in Gascony, in the south of France. Gascony was another major source of friction between the French and English crowns since the time of Edward's grandfather Edward I, but the English kings also had territorial claims to Normandy and other French regions dating back to the 12th century.
The Hundred Years War is usually divided into a number of phases. The first is the Edwardian phase (1337-60) which covers the famous campaigns of Edward III and his son Edward the Black Prince and the victories of Crecy and Poitiers. The War of the Breton Succession (1341-64) is an important sub-phase of this initial stage of the conflict, with England supporting John III's half-brother, John de Montfort, and France supporting the claim of Charles de Blois, nephew of the French king. Ironically, in the case of Brittany, the rival English and French kings were supporting the hereditary principles directly opposed to their own claim to the French throne! The capture of the French King John II at Poitiers in 1356 led to the temporary collapse of central authority in France. The subsequent 1360 Treaty of Brétigny effectively ended the initial phase of the Hundred Years War, with the English king receiving an extensive territory - effectively a much-enlarged Gascony – free from homage to the French crown. In return, the English King renounced his claim to the French crown itself. However, the treaty failed to secure a lasting peace.
While England and France were technically at peace during the 1360s, both powers intervened in the 1351-69 Castilian Civil War between Pedro I and his illegitimate half-brother Henry of Trastamara. To keep England safe from the powerful Castilian fleet, Edward III's son, Edward the Black Prince, who had taken part at Crecy and led the English army at Poitiers, led an army of English, Gascon and other mercenaries to assist Pedro I recover his throne. Meanwhile, Trastamara received assistance from France and the neighboring kingdom of Aragon. The Black Prince secured a decisive victory at Najera on 3 April 1367, but Trastamara survived and would later seize the Castilian throne, resulting in significant naval assistance for the French in subsequent decades. However, English support would later help prevent Portugal falling into Castilian hands in 1385.
The second phase of the Hundred Years War is termed the Caroline phase 1369-89, after the French king Charles V. With Edward III now old and the Black Prince ill, the French, supported by Castile, regained all the territory ceded to Edward III by the Treaty of Brétigny, not by winning decisive battles but mainly through Constable Bertrand du Guesclin's attritional strategy. Nevertheless, du Guesclin was ready to fight when a suitable opportunity arose and he could catch the enemy at a disadvantage, as at Pontvallain on 4 December 1370. The English naval defeat at La Rochelle in June 1372 had a major impact on the progress of the war, allowing du Guesclin to overrun the various small English garrisons in the territory ceded by the Treaty of Brétigny. By the 1380s, the conflict subsided into a virtual stalemate, with both England and France preoccupied by unrest and open revolt at home. The English King Richard II, who ruled until the usurpation of his cousin Henry Bolingbroke in 1399, secured peace with France in 1389 and married the French king's daughter. However, the usurper Henry IV's weak political hold on the English crown, led to revolts and enabled the French to recover much of Gascony.
The third and final phase of the Hundred Years War known as the Lancastrian phase 1415-53, lasted from Henry V's invasion of Normandy in 1415 and famous victory at Agincourt down to the final French reconquest of all the English continental possessions except Calais in the early 1450s. This phase, in turn, can be subdivided into the period from 1415 down to the Treaty of Troyes in 1420, the resurgence of the French under the inspirational Joan of Arc, and the final recapture of English-held Normandy and Gascony after two decisive English defeats at Formigny in 1450 and Castillon in 1453.
