While they had been securing the trade of the far Northwest and the Illinois country, the French had allowed the English to gain the trade of the upper Ohio,[152] and were now brought face to face with the danger of losing the entire Northwest, and thus the connection of Canada and Louisiana. The commandants of the western posts were financially as well as patriotically interested. In 1754, Green Bay, then garrisoned by an officer, a sergeant and four soldiers, required for the Indian trade of its department thirteen canoes of goods annually, costing about 7000 livres each, making a total of nearly $18,000.[153] Bougainville asserts that Marin, the commandant of the department of the Bay, was associated in trade with the governor and intendant, and that his part netted him annually 15,000 francs.

When it became necessary for the French to open hostilities with the English traders in the Ohio country, it was the Wisconsin trader, Charles de Langlade, with his Chippeway Indians, who in 1752 fell upon the English trading post at Pickawillany and destroyed the center of English trade in the Ohio region.[154] The leaders in the opening of the war that ensued were Northwestern traders. St. Pierre, who commanded at Fort Le Boeuf when Washington appeared with his demands from the Governor of Virginia that the French should evacuate the Ohio country, had formerly been the trader in command at Lake Pepin on the upper Mississippi.[155] Coulon de Villiers, who captured Washington at Fort Necessity, was the son of the former commandant at Green Bay.[156] Beaujeau, who led the French troops to the defeat of Braddock, had been an officer in the Fox wars.[157] It was Charles de Langlade who commanded the Indians and was chiefly responsible for the success of the ambuscade.[158] Wisconsin Indians, representing almost all the tribes, took part with the French in the war.[159] Traders passed to and from their business to the battlefields of the East. For example, De Repentigny, whose post at Sault Ste. Marie has been described, was at Michillimackinac in January, 1755, took part in the battle of Lake George in the fall of that year, formed a partnership to continue the trade with a trader of Michillimackinac in 1756, was at that place in 1758, and in 1759 fought with Montcalm on the heights of Abraham.[160] It was not without a struggle that the traders yielded their beaver country.