Why did Cornwallis surrender to yorktown

Well the french and indian war took place around 1754-1763 also they were pitted the colonies of british america against those of new france, each side supported by military units from the parent country by american indian it was a seven years war, but it ended with the treaty of paris in main point is that the british wanted to settle in the ohio river valley and to trade with native americans who lived there,so the french built forts to protect their trade with the indians,also in 1754, george washington led an army against the french! can finish it off(hope that (: