While actual clashes between Union and Confederate forces occurred in the American West, residents of that enormous region’s landscapes during the war years can be forgiven for using America’s internecine conflict to advance other interests and agendas. Although there can be little doubt of the intimate connection between westward expansion and the politics of slavery as well as the centrality of the West to the futures imagined by both Northern and Southern statesmen, the military conflict that dominated the country east of the Mississippi River barely touched the region. Little wonder that both scholars and ordinary Americans interested in the Civil War have traditionally spoken of the “western theater” in a manner that might confuse uninitiated readers. Yet one should not think that the American Civil War was irrelevant to westerners or that the West had no impact on the struggle between North and South. In fact, the American Civil War sharpened existing divisions within western states and territories, and provided the larger context for quickening transformations in the region’s politics, culture, economy, and society. At the same time, the West, though peripheral to the main theaters of war, loomed large in the strategic thinking of Union and Confederate leaders. Thus, an examination of the American West during the war years exposes tensions and outright contradictions: simultaneously committed and disengaged, westerners found that the conflict provided the perfect cover to address their perennial interest in controlling the pace and extent of Euro-American expansion. They could do so, moreover, wearing the uniforms of a federal government that before the war had sought to check or soften their expansionistic tendencies, an irony that was not lost upon contemporary observers.