Edward had inherited the duchy of Aquitaine, and as Duke of Aquitaine he was a vassal to Philip VI of France. Edward initially accepted the succession of Philip, but the relationship between the two kings soured when Philip allied with Edward's enemy, King David II of Scotland. Edward in turn provided refuge to Robert III of Artois, a French fugitive. When Edward refused to obey Philip's demands for the expulsion of Robert from England, Philip confiscated the duchy of Aquitaine. This precipitated war, and soon, in 1340, Edward declared himself king of France. Edward III and his son Edward the Black Prince, led their armies on a largely successful campaign across France.