Before then it was possible to picture a battle within the frame of a painting. It was not that artists ignored the horrors of war. Goya depicted the ravages of the decade-long Peninsular War in a series of engraving that have never been equalled for their honesty and their anger at what it was doing to victim and perpetrator alike. Turner took a particularly mournful view of the dead and dying that remained on the field of Waterloo the day after. But the portrayal of war was largely left in the hands of the celebrators of the victorious: Benjamin West, Jacques Louis-David and others. War was terrible but it was also heroic.
The American Civil War, from 1861 to 1865, changed all that. It was the first full-out conflict in which the mechanics and destruction overwhelmed the individual actions of men, the first to be fought in prolonged and unremitting trench
Article source: http://www.independent.co.uk/arts-entertainment/art/features/american-nightmare-the-art-of-the-civil-war-8430440.html