House of Plantagenet
Conflict with the House of Valois

In 1328, Charles IV of France died without a male heir. Queen Isabella made a claim to the throne of France on behalf of her son Edward, on the grounds that he was a matrilineal grandson of Philip IV of France. However, the precedents set by Philip V's succession over his niece Joan II of Navarre and Charles IV's succession over his nieces meant that the senior grandson of Philip III in the male line, Phillip of Valois, became king. Not yet in power, Edward paid homage to Phillip as Duke of Aquitaine.

In 1337, Phillip confiscated Aquitaine and Ponthieu from Edward, alleging he was harbouring Phillip's fugitive cousin and enemy, Robert of Artois. In response, Edward proclaimed himself king of France to encourage the Flemish to rise in open rebellion against the French king. The conflict, later known as the Hundred Years' War, included a significant English naval victory at the Battle of Sluys, and a victory on land at Crécy, leaving Edward free to capture the important port of Calais. A subsequent victory against Scotland at the Battle of Neville's Cross resulted in the capture of David II and reduced the threat from Scotland. The Black Death brought a halt to Edward's campaigns by killing perhaps a third of his subjects. The only Plantagenet known to have died from the Black Death was Edward III's daughter Joan in Bordeaux.

Edward, the Black Prince resumed the war with destructive chevauchées starting from Bordeaux. His army was caught by a much larger French force at Poitiers, but the ensuing battle was a decisive English victory, resulting in the capture of John II of France. John agreed to a treaty promising the French would pay a four million écus ransom. The subsequent Treaty of Brétigny was demonstrably popular in England, where it was both ratified in parliament and celebrated with great ceremony.

To reach agreement, clauses were removed that would have had Edward renounce his claim to the French crown in return for territory in Aquitaine and the town of Calais. These were entered in another agreement to be effected only after the transfer of territory by November 1361, but both sides prevaricated over their commitments for the following nine years. Hostages from the Valois family were held in London while John returned to France to raise his ransom. Edward had restored the lands of the former Angevin Empire, holding Normandy, Brittany, Anjou, Maine and the coastline from Flanders to Spain. When the hostages escaped back to France, John was horrified that his word had been broken and returned to England, where he eventually died.

Fighting in the Hundred Years' War spilled from the French and Plantagenet lands into surrounding realms, including the dynastic conflict in Castile between Peter of Castile and Henry II of Castile. The Black Prince allied himself with Peter, defeating Henry at the Battle of Nájera. Edward and Peter fell out when Peter was unable to reimburse Edward's military expenses, leaving him bankrupt. The Plantagenets continued to interfere, and John of Gaunt, 1st Duke of Lancaster, the Black Prince's brother, married Peter's daughter Constance, claiming the Crown of Castile in her name. He invaded with an army of 5,000 men; however, fighting was inconclusive, before Gaunt agreed to a treaty with King Juan of Castile. Terms of the treaty included the marriage of John of Gaunt's daughter Katherine to Juan's son, Enrique.

Charles V of France maintained the terms of the treaty of Brétigny but encouraged others in Aquitaine to challenge the authority of the Plantagenets in Aquitaine. The prince, who had suffered a debilitating illness for nearly a decade which often restricted his movement to being carried in a litter, returned to England, where he soon died. John of Gaunt assumed leadership in France with limited success, and peace negotiations over several years were inconclusive.
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