Initial campaign of the War of the Breton Succession

The initial campaign of the Breton Civil War took place in 1341 when a French royal army intervened in a succession war between two claimants to the Duchy of Brittany. Brittany was a province of France, but although the dukes of Brittany were vassals of the French kings they governed the duchy as independent rulers.

Source: Wikipedia — Initial campaign of the War of the Breton Succession (CC BY-SA 4.0)