War of the Breton Succession
Thomas of Woodstock was in command of a large campaign in northern France that followed the War of the Breton Succession of 1343–64. The earlier conflict was marked by the efforts of John IV, Duke of Brittany to secure control of the Duchy of Brittany against his rival Charles of Blois. John was supported in this struggle by the armies of the Kingdom of England, whereas Charles was supported by the Kingdom of France. At the head of an English army, John prevailed after Charles was killed in battle in 1364, but the French continued to undermine his position, and he was later forced into exile in England.