sentences:  Born out of commercial needs and located by the dictates of geography, the trails helped create and contribute to these international influences and the tensions which resulted.The United States sent military expeditions along the route of the trails to assert national interests in the face of the continued British presence in the northwestern fur posts on soil which the U.S. claimed.The Americans were also concerned about the establishment of Lord Selkirk's colony as well as British claims to the Red River Valley.