The Hundred Years' War was a series of conflicts that engulfed Europe between 1337 and 1453. Although the main opponents were England and France, other powers were often pulled into the conflicts. The main issue at stake had to do with a relationship between England and France dating back to the Norman conquest. Because of this history, England had territories in France and France claimed the monarch of England as a vassal. The end of the war settled many territorial claims.
Henry V's victory at the Battle of Agincourt in 1424 resulted in England gaining the upper hand in the war. Simultaneously, the heir to the French throne, the Dauphin (who was crowned as Charles VII), was in a politically precarious position, with the succession being called into doubt, with Henry VI of England having an equally strong claim to the French throne as the Dauphin.
Into this tumultuous situation, Joan of Arc claimed that religious visions sent her to support the Dauphin and led the French armies to several victories, beginning with freeing the besieged city of Orléans in 1429. Although she did not actually wield weapons or directly control tactics, her presence inspired the French to a series of victories and her enthusiasm for bold aggressive strategies changed the course of the war, switching the momentum to the French cause.
Joan of Arc was important in the Hundred Years’ War because somehow she managed to turn the tide of the war in favor of France. After she did this, the French were able to win the war, though it did drag on to some degree for decades after she was killed by the English.
By 1429, the French side was in bad shape in the Hundred Years’ War. They had suffered a huge defeat at Agincourt in 1415. They were led by Charles, the dauphin, who was not a very strong leader. Then English were besieging the city of Orleans and they would have gained access to the strategically important Loire valley if they won that siege.
It was then that Joan simply went to the dauphin’s court and somehow persuaded him to allow her to lead an army to relieve the siege at Orleans. She managed to make the army believe in her and she helped to lead them to victories that lifted the siege. This was a major turning point in the war. By helping to turn the war around, Joan of Arc was an important figure in the Hundred Years’ War.