The territory of the United States and its overseas possessions has evolved over time, from the colonial era to the present day. It includes formally organized territories, proposed and failed states, unrecognized breakaway states, international and interstate purchases, cessions, and land grants, and historical military departments and administrative districts. The last section lists informal regions from American vernacular geography known by popular nicknames and linked by geographical, cultural, or economic similarities, some of which are still in use today.
Unlike the land to the east, most of the land west of the Mississippi River was under French or Spanish rule until the first years of the 19th century.
La Louisiane (French Louisiana, 1682–1762 and 1802–1803)
Texas annexation; annexed from Mexico in 1846, including most of present-day Texas and parts of Oklahoma, Colorado, Wyoming and No Man's Land; disputed with Mexico until the end of the Mexican–American War in 1848
District of Columbia retrocession; the return to Virginia of the District of Columbia lands which Virginia had originally ceded for its creation, 1847.
Territory of Missouri (1812–1821); became the State of Missouri and unorganized territory (the eastern part of which was attached to the Territory of Michigan in 1834)
Territory of Minnesota (1849–1858) (preceded by unorganized territory of the original Northwest Territory (remnant of former Wisconsin Territory) and original Louisiana Purchase); split into the State of Minnesota and unorganized territory of the original Louisiana Purchase
Territory of Kansas (1854–1861) (preceded by unorganized territory of the original Louisiana Purchase); part became the modern State of Kansas; the western part became part of the Colorado Territory
Territory of Nebraska (1854–1867) (preceded by unorganized territory of the original Louisiana Purchase); split into the State of Nebraska, the Dakota Territory, additions to the Idaho Territory and additions to the Colorado Territory
Territory of Idaho (1863–1890) (preceded by parts of the territories of Washington, Dakota, and Nebraska); became the State of Idaho, the Montana Territory, additions to the Dakota Territory and additions to the Wyoming Territory.
The following are land grants, cessions, defined districts (official or otherwise) or named settlements made within an area that was already part of a U.S. state or territory that did not involve international treaties or Native American cessions or land purchases.
District of Louisiana; Missouri, Kansas, Iowa, Nebraska, Minnesota, North and South Dakota, Montana, Arkansas, Oklahoma, Colorado, Wyoming; renamed Missouri Territory in 1812.
These entities were sometimes the only governmental authority in the listed areas, although they often co-existed with civil governments in scarcely populated states and territories. Civilian administered "military" tracts, districts, departments, etc., will be listed elsewhere.
Department of the Missouri (1861–1865) Missouri, Arkansas, Illinois, part of Kentucky, and later Kansas; re-configured in 1865 as part of the Division of the Missouri.
District of California (headquarters at San Francisco, co-located with Department of the Pacific). Independent command from Department from (July 1, 1864 – July 27, 1865); those parts of California not in other districts.
The Department of California (1858–1861) comprised the southern part of the Department of the Pacific: California, Nevada, and southern part of Oregon Territory; merged into the Department of the Pacific as the District of California.
The Department of Oregon (1858–1861) comprised the northern part of the Department of the Pacific: Washington Territory and Oregon Territory.
Trans-Mississippi (or Trans-Mississippi Department; CSA) (1862–1865). Formerly "Military Dept. 2"; Missouri, Arkansas, Texas, Indian Territory (now Oklahoma), Kansas, and Louisiana west of the Mississippi River.
The west
Department of the West (1853–1861): all U.S. lands between the Mississippi River and the Military District of the Pacific not included in other Districts or Departments.
Kansas Territory (1854–1861) had two different governments in different cities, pro-slavery and anti-slavery, each claiming to be the real, lawful government of the entire territory. Since Kansas entered the union as a free state in 1861, there has only been one capital, Topeka, Kansas. It entered as a free state in 1861 because the entire pro-slavery block in Congress, which would not have allowed this, had left to become the Confederacy.
These are functioning governments created as a result of the attempted secession of the Confederacy during the American Civil War (1861–1865). Some were enclaves within enemy-held territories:
Belts are loosely defined sub-regions found throughout the United States that are named for a perceived commonality among the included areas, which is often related to the region's economy or climate.
Heidler, David Stephen; Heidler, Jeanne T.; Coles, David J.; Encyclopedia of the American Civil War: A Political, Social, and Military History; W. W. Norton & Company; New York; 2000; p. 590.