Hundred Years' War
Historians commonly divide the war into three phases separated by truces: the Edwardian War (1337–1360), the Caroline War (1369–1389), and the Lancastrian War (1415–1453). Local conflicts in neighbouring areas, which were contemporarily related to the war, including the War of the Breton Succession (1341–1365), the Castilian Civil War (1366–1369), the War of the Two Peters (1356–1369) in Aragon, and the 1383–85 crisis in Portugal, were availed by the parties to advance their agendas. Later historians adopted the term "Hundred Years' War" as a historiographical periodisation to encompass all of these events, thus constructing the longest military conflict in European history.
Brittany
The Breton War of Succession, a local episode of the Hundred Years' War, saw the House of Blois, backed by the French, fighting with the House of Montfort, backed by the English. The Montforts won in 1364 and enjoyed a period of total independence until the end of the Hundred Years' War, because France was weakened and stopped sending royal envoys to the Court of Brittany. English diplomatic failures led to the Breton cavalry commanders Arthur, Comte de Richemont (later to become Arthur III, Duke of Brittany) and his nephew Peter II, Duke of Brittany playing key roles on the French side during the deciding stages of the War (the Battle of Patay, the Treaty of Arras (1435), the Battle of Formigny and the Battle of Castillon). However, Brittany lost the Mad War against France in 1488, mostly because of its internal divisions which were exacerbated by the corruption at the court of Francis II, Duke of Brittany. Indeed, some Breton lords were fighting on the French side.