A comprehensive history of the achievements and failures of the U.S. Regular and Volunteer Armies in the two decades between the Mexican and Civil Wars, and an assessment of how the U.S. military policy and its implementation set the ground for the next half-century of westward expansion.

Manifest destiny and the army -- The mandate of Congress -- The Frontier Army, 1848-61 -- Garrisoning the Great Plains -- Occupying the Southwest -- Pacific outpost -- Rise of the Plains Indian Barrier, 1854-61 -- Rio Grande campaigns, 1854-61 -- Operations in the Pacific Northwest, 1855-60 -- Fort Sumter and the Western frontier -- The army of the Pacific, 1861-65 -- The army of the Southwest, 1862-65 -- Sibley, Sully, and the Sioux, 1862-64 -- Plains aflame, 1864 -- Plains campaigns, 1865 -- Legacy and prospect, 1866.