New Mexico Territory in the context of "San Elizario Salt War"

The Southwestern United States, also known as the American Southwest or simply the Southwest, is a geographic and cultural region of the United States that includes Arizona and New Mexico, along with adjacent portions of California, Colorado, Nevada, Oklahoma, Texas, and Utah. The largest cities by metropolitan area are Phoenix, Las Vegas, El Paso, Albuquerque, and Tucson. Before 1848, in the historical region of Santa Fe de Nuevo México as well as parts of Alta California and Coahuila y Tejas, settlement was almost non-existent outside of New Mexico's pueblos and Spanish or Mexican municipalities. Much of the area had been a part of New Spain and Mexico until the United States acquired the area through the Treaty of Guadalupe Hidalgo in 1848 and the smaller Gadsden Purchase in 1854.

While the region's boundaries are not officially defined, there have been attempts to do so. One such definition is from the Mojave Desert in California in the west (117° west longitude) to Carlsbad, New Mexico, in the east (104° west longitude); another says that it extends from the Mexico–United States border in the south to the southern areas of Colorado, Utah, and Nevada in the north (39° north latitude). In another definition, the core Southwestern U.S. includes only the states of Arizona and New Mexico; others focus on the land within the old Spanish and Mexican borders of the Nuevo México Province or the later American New Mexico Territory.

Arizona is a landlocked state in the Southwestern region of the United States, sharing the Four Corners region of the western United States with Colorado, New Mexico, and Utah. It also borders Nevada to the northwest and California to the west, and shares an international border with the Mexican states of Sonora and Baja California to the south and southwest. Its capital and largest city is Phoenix, which is the most populous state capital and fifth-most populous city in the United States. Arizona is divided into 15 counties.

Arizona is the sixth-largest state by area and the 14th-most-populous of the 50 states. It is the 48th state and last of the contiguous states to be admitted to the Union, achieving statehood on February 14, 1912. Historically part of the territory of Alta California and Nuevo México in New Spain, it became part of independent Mexico in 1821. After being defeated in the Mexican–American War, Mexico ceded much of this territory to the United States in 1848, where the area became part of the New Mexico Territory. The southernmost portion of the state was acquired in 1853 through the Gadsden Purchase.

The Texas panhandle is a region of the U.S. state of Texas consisting of the northernmost 26 counties in the state. The panhandle is a square-shaped area bordered by New Mexico to the west and Oklahoma to the north and east. It is adjacent to the Oklahoma Panhandle, land which Texas previously claimed. The 1820 Missouri Compromise declared no slavery would be allowed in states admitted from the Louisiana Purchase above 36°30′ north latitude. Texas was annexed in 1845 from still more westerly land. The Compromise of 1850 removed territory north of this line from Texas, and set the border between the Texas Panhandle and the New Mexico Territory at the 103rd meridian west. The eastern border at the 100th meridian west was inherited from the Adams–Onís Treaty of 1819, which defined the border between the United States and New Spain. The Handbook of Texas defines the southern border of Swisher County as the southern boundary of the Texas Panhandle region.

Its land area is 25,823.89 sq mi (66,883.58 km), or nearly 10% of the state's total. The Texas Panhandle is slightly larger in size than the US state of West Virginia. An additional 62.75 sq mi (162.53 km) is covered by water. Its population as of the 2010 census was 427,927 residents, or 1.7% of the state's total population. As of the 2010 census, the population density for the region was 16.6 per square mile (6.4/km). However, more than 72% of the Panhandle's residents live in the Amarillo Metropolitan Area, which is the largest and fastest-growing urban area in the region. Despite being geographically the northernmost part of Texas, the Panhandle is distinct from the region commonly called "North Texas", which is to the south and east.

Santa Fe de Nuevo México (English: Holy Faith of New Mexico; shortened as Nuevo México or Nuevo Méjico, and translated as New Mexico in English) was a province of the Spanish Empire and New Spain, and later a territory of independent Mexico. The first capital was San Juan de los Caballeros from 1598 until 1610, and from 1610 onward the capital was La Villa Real de la Santa Fe de San Francisco de Asís.

The name of "New Mexico", the capital in Santa Fe, the gubernatorial office at the Palace of the Governors, vecino citizen-soldiers, and rule of law were retained as the New Mexico Territory and later state of New Mexico became part of the United States. The New Mexican citizenry, primarily consisting of Hispano, Pueblo, Navajo, Apache, and Comanche peoples, became citizens of the United States as a result of the Treaty of Guadalupe Hidalgo (1848).

The Provisional Government of the Territory of Jefferson was an extralegal and unrecognized United States territory that existed in the Pike's Peak mining region from October 24, 1859, until it yielded to the new Territory of Colorado on June 6, 1861. The Jefferson Territory, named for Founding Father and third United States president Thomas Jefferson, included land officially part of the Kansas Territory, the Nebraska Territory, the New Mexico Territory, the Utah Territory, and the Washington Territory, but the region was remote from the governments of those five territories.

The government of the Jefferson Territory, while democratically elected, was never legally recognized by the United States government, although it managed the territory with relatively free rein for 19 months. Many of the laws enacted by the General Assembly of the Territory of Jefferson were reenacted and given official sanction by the new Colorado General Assembly in 1861.

The Territory of Colorado was an organized incorporated territory of the United States that existed from February 28, 1861, until August 1, 1876, when it was admitted to the Union as the 38th State of Colorado.

The territory was organized in the wake of the Pike's Peak Gold Rush of 1858–1862, which brought the first large concentration of white settlement to the region. The organic legislative act creating the free Territory of Colorado was passed by the United States Congress and signed by 15th President James Buchanan into law on February 28, 1861. This was during the onset of the American Civil War of April 1861 to June 1865. The boundaries of the newly designated Colorado Territory were essentially identical with those of the modern State of Colorado, with lands taken from the four surrounding previous Federal territories of Nebraska, Kansas, New Mexico, and Utah established during the 1850s. The organization of the new territory helped solidify Union control over the mineral-rich area of the western Rocky Mountains. Statehood was regarded as fairly imminent with the expected growth in the constantly westward moving population, but the local territorial ambitions for full statehood were thwarted at the end of the war in 1865 by a constitutional veto by newly sworn in 17th President Andrew Johnson (1808–1875, served 1865–1869), who was a War Democrat who succeeded to the office after briefly only serving one month as Vice President after Lincoln's assassination that April. Statehood for the territory was a recurring issue during the subsequent Ulysses S. Grant presidential administration, with Republican 18th President Grant advocating statehood against a less willing Congress during the following post-war Reconstruction era (1865–1877). After a long constant lobbying campaign, the old Colorado Territory finally ceased to exist after only 15 years when the State of Colorado was admitted to the Union as the 38th state during the American Centennial celebration in August 1876.