In The Spirit of War, a rugged mountain landscape provides the backdrop for a medieval wartime scene, all bathed in an eerie, fiery light: knights on horseback ride into battle, a distant settlement burns, and a mother and child cower on the ground. A medieval castle rises from the jagged rocks, its looming tower framed by gathering storm clouds that portend destruction. The artist himself described the fraught scene as "promising naught but the uncertain and gloomy future of warlike times." By contrast, its companion piece The Spirit of Peace (Philadelphia, Woodmere Art Museum), shows an Arcadian landscape with tiny figures engaged in various pastoral pursuits. The center of the composition is anchored by a circular temple containing symbols of peace. Clear skies, the soft light of sunset, and placid waters convey tranquility and prosperity. Praised for their narrative clarity and displaying Cropsey's fondness for detailed nature studies, the allegorical pair went on to become the most exhibited of his works.
The paintings' twinned themes of war and peace expressed as historical allegories would have had an immediate emotional significance for Cropsey's audience. The recent Mexican War (1846-1848) and the subsequent debate over whether the western territories would join the nation as free or slave states contributed to the strained national atmosphere in the decade preceding the Civil War. First shown as his New York studio, this allegorical pair were shown seven times between 1852 and 1857. In this carefully constructed tour de force the earnest young artist created a powerful and lasting image of the fear and hopelessness brought about by war, eerily foreshadowing the bloody conflict that would envelop his country in the following decade.
More information on this painting can be found in the Gallery publication American Paintings of the Nineteenth Century, Part I, pages 110-114, which is available as a free PDF at https://www.nga.gov/content/dam/ngaweb/research/publications/pdfs/american-paintings-19th-century-part-1.pdf