The establishment of Fort Oswego (modern Oswego, New York) in the 1720s on the south shores of Lake Ontario (called Lac de Frontenac by the French) represented the first British toehold in what until then had been a "French lake", and was regarded as a major threat by the French. The French had dominated the Great Lakes and with it the lucrative fur trade, and were determined to keep the Great Lakes for themselves. However, the 1720s-30s were a period of Anglo-French detente in Europe with both the duc d'Orleans, the Regent for the boy king Louis XV in France, and Prime Minister Sir Robert Walpole in Britain, being committed to a policy of peace. Through the French protested at the establishment of Fort Oswego, saying the Great Lakes were part of New France, neither Paris nor London wanted a war over a fort in far-away North America, and so the matter rested for the moment. Versailles and Whitehall both agreed to an understanding that the British would not build any more forts on the Great Lakes in exchange for which the French tolerated Fort Oswego. Fort Oswego was a remote frontier post located in the wildness, and in the words of the Canadian historian René Chartrand its "Achilles heel" was its supply lines. The period of Anglo-French detente and peace which both Walpole and the duc d'Orleans pursued gave way to a period of war in the middle 18th century. France and Britain went to war in the inconclusive War of the Austrian Succession which was followed by the Seven Years' War, which began in North America in 1754 when the Virginia militia under the command of George Washington made a very unsuccessful attempt to expel the French from the Ohio river valley.