Origins
The war originated in the dynastic crisis that followed the death of the French king Charles IV in 1328 without male heirs. The English king Edward III, son of Isabella of France and grandson of the French king Philip IV, had the strongest direct blood claim. The French nobility, however, applied the Salic Law — a body of Frankish customary law that excluded inheritance through the female line — and gave the crown to Philip VI of Valois, Charles IV’s cousin.
Edward III initially accepted the Valois succession and performed feudal homage for the Duchy of Gascony (the English-held territory in southwestern France) in 1331. The relationship deteriorated through the 1330s over disputed feudal jurisdiction in Gascony, French support for Scottish raids on northern England, and English support for Flemish revolts against French rule. In 1337 Philip VI declared Edward’s Gascon holdings forfeit. Edward III responded by formally claiming the French throne.
The war that followed lasted 116 years through long periods of truce.
The English phase, 1337–1380
The first phase of the war was a series of English military successes. The longbow proved decisive in three major battles — Crécy (1346), Poitiers (1356), and (much later) Agincourt (1415) — against numerically superior French armies. The Black Prince’s army captured King John II of France at Poitiers in 1356; John II was ransomed for 3 million gold écus, an enormous sum that the French struggled to pay.
The Treaty of Brétigny (1360) gave England full sovereignty over Aquitaine, Poitou, and Calais. Edward III renounced his French throne claim in exchange.
The war then paused while the Black Death ran through both countries, killing approximately a third of each population.
The Caroline phase, 1369–1389
War resumed in 1369 under Charles V of France, who systematically reconquered most of the English holdings using a strategy of avoiding pitched battles and instead waging slow attritional warfare. By 1380 the English held little more than coastal Aquitaine and Calais.
The Lancastrian phase, 1415–1453
The most spectacular English victory of the war — Henry V’s defeat of the French at Agincourt on 25 October 1415 — opened the final phase. Henry V’s subsequent campaigns reduced northern France to English control by the Treaty of Troyes (1420), which made Henry V the heir to the French throne. Henry V died in 1422 before he could inherit, leaving the infant Henry VI to be crowned king of both England and France.
The recovery of France from this nadir is associated with Joan of Arc, the peasant girl from Lorraine who claimed divine visions and led French forces to lift the siege of Orléans in 1429. Charles VII was crowned king of France at Reims later that year. Joan was captured by the Burgundians (English allies) in 1430, sold to the English, tried for heresy, and burned at the stake on 30 May 1431.
The French recovery continued through the 1430s and 1440s. The Battle of Castillon (17 July 1453) — the first major European battle in which gunpowder artillery was decisive — destroyed the last English field army in Gascony. The English crown lost all its French territories except Calais.
Consequences
England and France emerged as recognizably modern nation-states with strong centralised monarchies. The English aristocracy, having lost its French holdings, turned inward and produced the Wars of the Roses (1455–1487) almost immediately afterward. The French monarchy became the dominant power in western Europe for the next three centuries.
The longbow, the codified rules of chivalric warfare, the use of mercenary companies, the gunpowder cannon, and the early forms of national identity all developed substantially during the war. Calais remained English until lost to the French in 1558 under Mary I.