The Photographic History of The Civil War: in ten volumes, Thousands of Scenes Photographed 1861-65, with Text by many Special Authorities, Volume 1: The Opening Battles.
Francis Trevelyan Miller, Ed.

The War of the States was viewed at first with indifference by foreign military men. For many years past, however, it has claimed their close attention, because they have come to realize that new conditions were tested then, and that new influences, which changed the art of the general even from the respected models of Napoleon fifty years before, were at work. Ironclads, entrenchments, railroads, the breech-loader, a new kind of cavalry were the fresh factors in the problem.

Although hostilities at first began over an area half as large as Europe, the region of decisive operations was, on account of lack of communication, narrowed to the country between the Atlantic and the Mississippi, about seven hundred miles in an air-line. The line was unequally divided by the towering barrier of the Alleghany Mountains, about two hundred miles wide, over which communication was difficult. The eastern section of the country beyond the range was about one hundred miles wide and the western section was about four hundred miles wide. In Maryland, northwestern Virginia, Kentucky, and Missouri sentiment was divided between the Union and the Confederacy. The Mississippi River separated three of the seceding States from the remaining eight.

The immense amount of supplies needed for a great army caused military operations on a large scale to be confined to rail and water lines. Of the former, both the North and South had several routes running east and west for lateral communication, and the South had several running north and south in each section, which could be used for lines of military-operations. In respect to water routes, the North soon demonstrated its complete control of the sea and was thus able to choose its points of attack, while interior water routes were available by the Mississippi, Tennessee, Cumberland, and James rivers. The advantage of the water route over that by rail was at once utilized by the Northern generals.