As a result of the Hundred Years' War, England lost all of its territory in France except for the northern port city of Calais. It also contributed to nationalism, as France and England began to see themselves as more than as a collection of provinces.
Periodic fighting over the English rights to territories in France dated back to the 12th century. However, the Hundred Years' War started in earnest when the French king Charles IV died in 1328. King Edward III of England had a legal claim to the French throne because his mother was the late king's sister. He deferred to Philip VI, a Frenchman from a younger branch of the family, but when Philip VI tried to seize some of Edward's French territory in 1337, the English king renewed his claim and backed it up with troops.
Though outnumbered and relatively poor, the English army initially saw huge victories, such as the Battle of Crecy, in which the English used new tactics and technology, such as the longbow, to defeat the French cavalry. These victories helped them secure the Treaty of Calais of 1360, which granted the English significant tracts of land while requiring the English king to renounce all claims to the French throne. However, when King John died in 1364, his son, Charles V, repudiated the treaty and renewed the war. Over the decades, the French took back their land, and the war petered out.