The Hundred Years War
The English had been conquered and ruled by a French feudal lord from Normandy by the name of William the Conqueror. Because William the Conqueror had been a powerful leader in Normandy, he claimed both England as well as much of France as his kingdom.
Later English kings maintained their right to rule parts of France. This created a great deal of resentment for both the French people as well as their kings, who wanted control of their lands back.
In 1152 A.D., King Henry II of England married Eleanor of Aquitaine. Eleanor was the heiress to much of the lands in the southwest of France. This gave King Henry II control over more of France than the French king had.
In 1328 A.D., when the king of France died without leaving a direct heir, the situation became dangerous. King Edward III of England was the grandson of the former French King. As such, he was the rightful successor to the French throne. This gave King Edward III the right to rule both England and France from a single throne.
The French were not ready to be ruled by an English King. Feelings between the English and French were too bitter. A Frenchman by the name of Philip of Valois, who was the nephew of the former king of France, began preparations for war with England, a war that would last from 1337 until 1453 A.D.
At first, it appeared as though England would win the war. Their superior technology and strategies led them to victory in a series of battles where they were often out numbered by the French. Eventually, however, the tables would be turned.
After more than one hundred years of fighting, the French were eventually able to declare victory over the English.
The One Hundred Years War greatly strengthened France, while weakening England. Following the war, England would enter a period of turmoil and civil war that would last for another 30 years.