John V, sometimes numbered as VI, bynamed John the Wise, was Duke of Brittany and Count of Montfort from 1399 to his death. His rule coincided with the height of the Hundred Years' War between England and France. John's reversals in that conflict, as well as in other internal struggles in France, served to strengthen his duchy and to maintain its independence.

The Hundred Years' War was a series of armed conflicts fought between the kingdoms of England and France during the Late Middle Ages. It originated from English claims to the French throne initially made by Edward III of England. The war grew into a broader military, economic, and political struggle involving factions from across Western Europe, fueled by emerging nationalism on both sides. The periodization of the war typically charts it as taking place over 116 years. However, it was an intermittent conflict which was frequently interrupted by external factors, such as the Black Death, and several years of truces.