It is important to note that the Hundred Years’ War did not last for exactly one hundred years. The actual timeline is considered to be from 1337 to 1453. It was a war where the world witnessed the British-French conflict which would go on, way beyond this war period.
The Hundred Years’ War was not a continuous struggle; in fact, it was more intermittent. There was always some conflict between the British and the French regarding the title of the crown. So, the English kings had their own ways regarding the inheritance of the crown, and similarly, the French had their own.
The problem arose in 1328, after the death of French King Charles IV. Edward III of England claimed his inheritance for the throne, as he had a family relationship with Charles IV, and also the fact that the latter had no sons left behind him. The matter was settled as the French assembly decided to choose Philip VI for the throne. Even Edward III accepted it for the time being.
However, in 1337, when Philip VI tried to seize control of Guyenne (Edward III was the duke of Guyenne), Edward III once again began to reclaim the French throne and brought his army. The struggle, thus started, was passed on to the next generations and only stopped after 1453 when conquered most of the region.