Hundred Years’ War

 ... was an intermittent struggle between England and France in the 14th–15th century over a series of disputes over territories & the question of the legitimate succession to the French crown:

• As the English kings started as Dukes of Normandy, their continental territories were a constant source of conflict.
• When the last Capet dynasty died without an heir, the English king Edward III claimed to have the rightful ruler of France over the newly Valois king, Philip the VI.

Initially, the English won quite a few battles but failed to unite England and France under one crown.