Today Brittany is the northwestern province of France that pokes out into the sea. In the Middle Ages however, it was a duchy struggling to maintain its independence. Although bordering French territories, it had more in common with the nearby British Isles. England and Brittany shared a strong Celtic culture, the legends of King Arthur, and even the names of cities and places.
In the middle of the fourteenth century, Brittany was torn apart by civil war. In 1341 the duke died, leaving no children to succeed him. Two of his relatives claimed the ducal crown. One was Jean Comte de Montfort, the dead duke’s half-brother. The other was a woman, Jeanne de Penthievre, who was married to Charles de Blois, a nephew of the French king.
England supported the Montfort succession while France supported the Penthievre. The two great nations became involved in a ferocious war that ravaged Brittany. The death of Jean Comte de Montfort did not end things. His wife continued the fight in her son’s name. Charles de Blois’s wife did the same after he was captured by the English.
In the midst of this chaos, a new threat appeared. In 1348 the plague known as the Black Death began its first devastating sweep through Europe.
Brittany was France’s Scotland, choleric, Celtic, stony, bred to opposition and resistance, and ready to use the English in its struggles against its overlord as the Scots used the French in theirs.
--Barbara Tuchman, A Distant Mirror