In the perspective of military history the Civil War is the first modern war. It marked a transition from the older warfare, which involved principally the fighting forces, to the modern which affects in varying degree every group of society and which would demand ultimately a totalisation of national life. The Civil War was a war of material as well as of men. It witnessed the innovation or employment of mass armies, railroads, armoured ships, the telegraph, breech-loading and repeating rifles, various precursors of the machine-gun, railway artillery, signal balloons, trenches, and wire entanglements. It was a war of ideas and therefore of unlimited objectives. One side or the other had to win a complete victory: the North to force the South back into the Union, the South to force the North to recognise its independence. There could be no compromise, no partial triumph for either. In contrast to the leisurely, limited-objective wars of the eighteenth century, the Civil War was rough, ruthless and sometimes cruel.

It was the first great military experience of the American people and their greatest historical experience. The drama, the agony, the valour of the years 1861–5 became a permanent part of the national consciousness. So did a profound realisation of its significance. In American history the Civil War is the great pivotal event, comparable to the revolution of 1789 in France. It settled certain differences, and it settled them permanently. It destroyed slavery, and assured the ascendancy of industrial capitalism. Furthermore, it preserved the Union and stabilised, if it did not indeed create, the modern American nation.