The 100 Years' War was actually a series of conflicts between France and England that began in 1337 and ended in 1453. Two royal houses fought for the French throne, which was vacant with the extinction of the Capetian line of French kings.

A major cause of the conflict was the fight for control of the English possessions in southwest France.

The war began in earnest with Edward III claiming to be not only King of England but King of France as well. Although the English won most of the battles; the war ended with England losing all its territory on the continent, except for Calais.

Historically the war was important because it strenghtened English national consiousness; English culture became distinct from French.
It also marked the decline of feudalism, the rise of French unity, the development of the French national state, and the growth of English sea power.

But shorn of its Continental possessions, England was left an island nation, a fact which profoundly affected its outlook for more than 500 years.

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100 Years War History Page