In 1337, Philip VI of France confiscated the English king's Duchy of Aquitaine and the county of Ponthieu. Instead of seeking a peaceful resolution to the conflict by paying homage to the French king, as his father had done, Edward responded by laying claim to the French crown as the grandson of Philip IV. The French rejected this based on the precedents for agnatic succession set in 1316 and 1322. Instead, they upheld the rights of PhilipIV's nephew, King PhilipVI (an agnatic descendant of the House of France), thereby setting the stage for the Hundred Years' War (see family tree below). In the early stages of the war, Edward's strategy was to build alliances with other Continental rulers. In 1338, Louis IV, Holy Roman Emperor, named Edward vicar-general of the Holy Roman Empire and promised his support. As late as 1373, the Anglo-Portuguese Treaty of 1373 established an Anglo-Portuguese Alliance. These measures produced few results; the only major military victory in this phase of the war was the English naval victory at Sluys on 24 June 1340, which secured its control of the English Channel.