The war known as the Hundred Year War was in fact a series of conflicts over the Crown of the Kingdom of France between two dynasties.
As was edicted in the Salian Law, the heir to the French throne had to be a descendent of a previous king exclusively through male lineage. That made the house of Valois the legitimate ruler at the time. The king of England, of the House of Plantagenet, was linked many times through marriage to all the great families of France. He was at that time the largest land owner in the Kingdom. He considered that the crown was his, but the Salian Law prohibited that. Ensued many years of conflict that lasted from 1337 to 1453. The Valois dynasty prevailed ultimately thanks to the courage of a teenage girl, Joan of Arc, who had a vision that only she could "boot out the English". Her pledge was successfully leveraged by the young Valois king and galvanized the population to take arms. This tilted the balance in favour of the Valois, although Joan herself was made prisoner and burnt at the stake for heresy in 1431. Ultimately, the English king lost all his possessions and the war came to an end in 1453.