In Brooklyn and Manhattan, Whitman observed and cataloged the vibrant city landscape. More than a decade before the Civil War erupted, Whitman traveled extensively and encountered both the expansive landscapes of the western United States and some of the darker parts of the country's character, witnessing New Orleans' booming slave trade firsthand. During the Civil War, Whitman supported the Union cause, working as a nurse in the hospitals of Washington, D.C. These experiences, undisguised and unadorned, found their way into Leaves of Grass.