The Hundred Years' war started when King Edward III claimed to be the heir to the French throne. There were many weird marriage contracts and he was the relative of the former King of France.
I, King Edward III of England, am the rightful heir to the French throne.
At the Battle of Agincourt, the English ticked the French into attacking. This gave the English enough time to set up a wall of pointed stakes and rows of skilled bowmen with longbows in their hands. As the French began to attack, the English shot them down with their longbows. This turned the tide of the Hundred Years' War to the advantage of the English.
Joan of Arc believed that young Charles, son the King Charles, deserved to be king. She told him that the saints and angels told her that he was the rightful king of France. She convinced him to allow her to lead an army into Orleans.
You must allow me to lead an army into Orleans. This is the only way to save France.
The Siege of Orleans was lead by Joan of Arc. She rode up on her horse to the English and told them that the saints and angels would kill them all. She drove the English out of Orleans turning the tide of the war again, but this time to the French.
Turn back now before I use God's power to wipe out your army.
At the Battle of Castillon, the French convinced the English to attack. This gave them time to set up their cannons. The overall battle took about 5 hours making it one of the shortest battles in the Hundred Years' War. The French won pretty much ending the Hundred Years' War.
At the end of the war the French drove the English out of their land. Each country pretty much had the exact same amount of land by the end of the war. Also feudalism was replaced by nationalism. This began the age of exploration and a new era called the Renaissance.