The status of the English kings' French fiefs was a major source of conflict between the two monarchies throughout the Middle Ages. French monarchs systematically sought to check the growth of English power, stripping away lands as the opportunity arose. Towards the end of 1336, following a series of disagreements between Philip VI of France () and Edward III of England (), Philip decided that war was the only way to drive the English out for good. On 24 May 1337, Philip's Great Council in Paris agreed that the Duchy of Aquitaine, effectively Gascony, should be taken back into Philip's hands on the grounds that Edward was in breach of his obligations as a vassal. This marked the start of the Hundred Years' War, which was to last 116 years.