After the fall of Memphis, New Orleans, and Baton Rouge, the Confederates were left in possession only of that part of the Mississippi river which lies between Vicksburg and Port Hudson. Their possession of that stretch of river was doubly important to them. Defensively, it enabled them to blockade the river and render it a no-thoroughfare to Federal troops and supplies. Still more importantly, it enabled them to maintain their communications with the country lying to the west of the Mississippi in Arkansas, Louisiana, and Texas. From that region they drew a very important part of their food supplies. These came to Vicksburg by water or over the Shreveport railroad on the west of the river, and were carried from Vicksburg eastward by other lines of railroad. A still more important line of communication was that by way of the Red river, which empties into the Mississippi from the westward between Vicksburg and Port Hudson. To hold these routes seemed almost an absolute necessity to the Confederates. To cut them and open the Mississippi river from Cairo to the Gulf was equally a necessity to the Federals. Here were the conditions that rendered a campaign inevitable, and in a degree marked out its course and character. The Confederates energetically fortified Vicksburg and Port Hudson, and planted posts at various other points on both sides of the Mississippi and on the Arkansas and Red rivers. The Federals had made several attempts--one of them made by Farragut himself--to open the Mississippi, but had completely failed, largely because the Confederate fortifications at Vicksburg were perched so high upon the bluff that Farragut's guns could not be sufficiently elevated to reach them. It was not until the twelfth of November, 1862, that General Grant was set free to do those things which it was necessary to do in this quarter of the country. On that date he received a dispatch from General Halleck, giving him command of all troops in his department, and authorizing him to conduct operations there on his own judgment. Thus armed with liberty to act, Grant instantly consulted Sherman, in whose sagacity and in whose superb fighting qualities he had the utmost confidence. These two energetic commanders quickly agreed upon a plan of action which looked to nothing less than the capture of Vicksburg and Port Hudson, the opening of the great river throughout its length, and the severance of the Confederacy in twain.