... West to the mouth of the Rio Grande; and inland over the course of the Mississippi, and itsaffluents, from Cairo, at the southern extremity of the State of Illinois, to the mouths of the river.Key ... of the prime object the control of the Mississippi Valley.Before the war the Atlantic and Gulf waters of the United States, with those of the West Indies, Mexico, andCentral America, were the ... was devoted to the cause of the Union, but the allegiance of the two others, both slave-holding, was very doubtful at the time of the outbreak of hostilities. The general course of the Mississippi...