The United States gained vast territories in the West through the Mexican War of 1846−48 and the 1846 Oregon Treaty with Great Britain. By the early 1850s, government and commercial interests were debating the possibilities of building a transcontinental railroad to the Pacific. The Army Appropriations Act of 1853 provided for the completion of railroad surveys to determine possible routes. This map, issued in 1858 by Secretary of War Jefferson Davis, depicts the United States west of the Mississippi on the eve of the Civil War. California and Texas were at this time the only Western states. Western regions initially became part of the United States as military departments, which only later were organized into territories and, eventually, states. The map uses colors to show the military departments and Indian lands. Brown flags indicate military establishments. In the lower right are listed all of the important surveys and expeditions that contributed to the mapping of the West, from the Lewis and Clark Expedition of 1804 to a survey of roads between the Sacramento and Columbia Rivers undertaken by two army officers in 1855. The routes of these expeditions are shown on the map. The map was compiled by then-Lieutenant Gouverneur K. Warren of the Army Topographical Engineers and a future Union general in the Civil War. Davis later became president of the Confederacy and a bitter adversary of President Abraham Lincoln under whose leadership, ironically, work on the transcontinental railroad began in 1862.