"Westward expansion" redirects here. For trails in the American Old West, see Westward Expansion Trails.
Animated map of the territorial evolution of the United StatesUS Census Bureau map depicting territorial acquisitions, 2007After Japan's defeat in World War II, the Japanese-ruled Northern Mariana Islands came under control of the United States.[1]
The first great expansion of the country came with the Louisiana Purchase of 1803, which doubled the country's territory, although the southeastern border with Spanish Florida was the subject of much dispute until it and Spanish claims to the Oregon Country were ceded to the US in 1821. The Oregon Country gave the United States access to the Pacific Ocean, though it was shared for a time with the United Kingdom.[2] The annexation of the Republic of Texas in 1845 led directly to the Mexican–American War, after which the victorious United States obtained the northern half of Mexico's territory, including what was quickly made the state of California.[3]
As the development of the country moved west, however, the question of slavery became more important, with vigorous debate over whether the new territories would allow slavery and events such as the Missouri Compromise and Bleeding Kansas. This came to a head in 1860 and 1861, when the governments of the southern states proclaimed their secession from the country and formed the Confederate States of America. The American Civil War led to the defeat of the Confederacy in 1865 and the eventual readmission of the states to the United States Congress. The cultural endeavor and pursuit of manifest destiny provided a strong impetus for westward expansion in the 19th century.
The United States began expanding beyond North America in 1856 with the passage of the Guano Islands Act, causing many small and uninhabited, but economically important, islands in the Caribbean Sea and the Pacific Ocean to be claimed.[4] Most of these claims were eventually abandoned, largely because of competing claims from other countries. The Pacific expansion culminated in the annexation of Hawaii in 1898, after the overthrow of its government five years previously. Alaska, the last major acquisition in North America, was purchased from Russia in 1867. Support for the independence of Cuba from the Spanish Empire, and the sinking of the USS Maine, led to the Spanish–American War in 1898, in which the United States gained Puerto Rico, Guam, and the Philippines, and occupied Cuba for several years. American Samoa was acquired by the United States in 1900 after the end of the Second Samoan Civil War.[5] The United States purchased the U.S. Virgin Islands from Denmark in 1917.[6] Puerto Rico and Guam remain territories, and the Philippines became independent in 1946, after being a major theater of World War II.
States have generally retained their initial borders once established. Only three states (Kentucky, Maine, and West Virginia) have been created directly from area belonging to another state (although at the time of admission, Vermont agreed to a monetary payment for New York to relinquish its claim); all of the other states were created from federal territories or from acquisitions. Four states (Louisiana, Missouri, Nevada, and Pennsylvania) have expanded substantially by acquiring additional federal territory after their initial admission to the Union. In 1912, Arizona was the last state established in the contiguous United States, commonly called the "lower 48". In 1959, Hawaii was the 50th and most recent state admitted.
Legend for maps
Key to map colors
United States states (domestic maps), undisputed area of United States (dispute maps)
Many states had vaguely defined and surveyed borders; these are not noted as contested in the maps unless there was an active dispute. The borders of North Carolina were particularly poorly surveyed, its border with South Carolina having been done in several pieces, none of which truly matched the spirit of the charter,[27][28] and its border with Virginia was only surveyed roughly halfway inland from the sea.
Several northeastern states had overlapping claims: Connecticut, Massachusetts Bay, and New York all claimed land west of their accepted borders, overlapping with each other and with a sizable claim by Virginia. Of the three, only Connecticut seriously pursued its claims, while Virginia is considered to have had the most legitimate claim to the vast northwest, dividing it into counties and maintaining some limited control.
The entirety of the new United States was claimed by Great Britain, including Machias Seal Island and North Rock, two small islands off the northeast coast which remain disputed up to the present.[29]
Vermont claimed what was called the "East Union", consisting of some towns in New Hampshire that petitioned on March 12, 1778, to join with Vermont, out of concern that their state was focusing too much on its coastal region. Vermont never gained full control over the area.[32][35][36][37][b]
Disputes:
October 21, 1778
Under pressure from the Continental Congress, Vermont rescinded the annexation of the East Union; the legislature declared on February 12, 1779, that the East Union should be considered null from its beginning.[35][36][37]
North Carolina and Virginia surveyed their border further inland. Virginia's survey reached the Tennessee River on this date,[39] while North Carolina's team stopped at the Cumberland Gap and filed their survey on November 17, 1779.[40] The two surveys were roughly two miles apart, creating a thin area claimed by both states. While the border was intended to follow 36°30′ north, early surveying errors caused it to veer north of that, reaching a distance of almost ten miles off by the time it reached the Tennessee River.[41][24]
Vermont again claimed an East Union, consisting of some towns in New Hampshire that wished to join with Vermont; more towns were interested than during the first attempt in 1778, though again, the exact extent of the borders is unknown. Vermont never gained full control over the area.[32][43][36][37][c]
Disputes:
June 16, 1781
Vermont claimed what was called the "West Union", consisting of some towns in New York, mainly to counterbalance Vermont's attempt at eastward expansion. Vermont never gained full control over the area.[32][36][44][45] The specific date this occurred is unclear; sources suggest June 16, June 26, and July 18.[d]
The federal government accepted the cession from New York of its western claims, which the state ceded on February 19, 1780, and executed on March 1, 1781; New York proclaimed its new western border to be a line drawn south from the western end of Lake Ontario. At its maximum interpretation, the state had claimed an area bounded by Lake Erie, Lake Huron and Lake Michigan; to the Illinois, Mississippi, and Tennessee Rivers; and north along the Appalachian Mountains, ending at the border with Pennsylvania.[47] It is unclear from where this claim came; many sources state that New York had surrendered it, but very few elaborate on how it was obtained. One source states that it was a cession by the Six Nations, who had conquered much of the region.[48] However, New York never seriously enforced these claims. The cession included the small tip of New York north of Pennsylvania, which came to be known as the Erie Triangle.[49][18]
December 30, 1782
The Congress of the Confederation declared that the land that Connecticut claimed in northern Pennsylvania, a westward extension of Connecticut's borders, was part of Pennsylvania, thus attempting to end the Pennamite–Yankee War.[50][20] While conflict would continue for some time, this was the end of the formal claim by Connecticut.
The border extending from Lake Superior towards the Lake of the Woods was poorly defined as starting from "Long Lake", which both sides interpreted to their advantage.
The Peace of Paris also involved treaties with France and Spain, with Great Britain ceding the Floridas to Spain. During their ownership of West Florida, the British had moved its border north, and the cession to Spain appeared to apply to the full extent of the British colony. However, the British-American treaty granted the extension of West Florida to the United States, where it enlarged Georgia south to 31° north, indicating that only the original definition of West Florida was to be ceded to Spain. The local Spanish governors also made a move to occupy forts along the Mississippi River, with claims to everything south of the Tennessee River; it is unknown how official or strong these claims were, and they are not mapped as they are in conflict with the other Spanish claim involving the border of West Florida.[54]
Disputes:
1784–1803 (Organization of territory)
Date
Event
Change Map
August 23, 1784
A region in central North Carolina (modern-day eastern Tennessee), unhappy with the state's governance over the area, declared independence from the state as the State of Franklin.[f][56][57] The government of Franklin held some control over the area, and petitioned for statehood, receiving support from seven of the nine states required, but would only last a few years.[58][59]
The federal government accepted the cession from Massachusetts of its extreme western claim, which was never seriously enforced.[g][47][14]
Change on paper only:
September 13, 1786
Connecticut surrendered its western claim to the federal government except for its Western Reserve, though it is unclear how much control they held over the ceded region.[h][9][60]
South Carolina ceded its western claim to the federal government,[63][23] though it was a result of inaccurate geography and South Carolina never actually held claim to this land. The claim was of a strip of land between the border of North Carolina and the source of the Tugaloo River but, unknown at the time, the river originated in North Carolina. The eastern part of this cession would be given to Georgia in 1802, despite Georgia technically already having claim to the land.[64]
New Hampshire became the ninth state to ratify the Constitution;[73] at this point, the Constitution became the active governing document of those nine states having ratified the same (per Article VII).
The District of Columbia, a federal district planned to house the federal government by 1800, was formed from land ceded by Maryland and Virginia,[84][85] consisting of a 100 square mile diamond, with its southern tip at Jones Point, straddling the Potomac River. However, it was not yet given that name, being simply referred to as the federal district. In September 1791, the commissioners in charge of planning the city would term it the "Territory of Columbia", and various laws refer to a District of Columbia, but sometimes informally. The area does not appear to have been formally named "District of Columbia" until at least the organic act of 1871.[86] Since the name "Columbia" was used from very early on, and at least informally by the government, the map will use "District of Columbia" starting from this date.
The western half of Virginia, which the state had agreed in 1789 to cede to the federal government,[87] was admitted as the fifteenth state, Kentucky.[l][89][88]
In response to the Yazoo Land Fraud, an act authorized President John Adams to appoint commissioners to negotiate with Georgia about ceding its western land. The act created Mississippi Territory from the southwestern quarter of Georgia in the region recently ceded by West Florida, while maintaining that Georgia still held rights over the territory.[96][97]
October 25, 1798
Commissioners agreed on the source of the St. Croix River, setting the lower portion of the border between Massachusetts and Great Britain and, thus, where the eastern north–south line originated.[98]
Disputes:
June 9, 1800
Connecticut ceded its Western Reserve to the federal government, which assigned it to the Northwest Territory.[99] The act doing so was passed in Congress on April 28, 1800, and Connecticut approved it on this date.[100]
Georgia ceded its western half, known as the Yazoo Lands, to the federal government.[n] At the same time, the federal government ceded to Georgia the eastern portion of the land previously ceded by South Carolina, though in reality Georgia technically already held title to the land, as the description of the earlier cession was based on an erroneous understanding of geography.[12]
March 1, 1803
The southern half of the Northwest Territory, along with a thin sliver of Indiana Territory, was admitted as the seventeenth state, Ohio. The remainder of the Northwest Territory was transferred to Indiana Territory.[106][61] The western border was a line due north from the mouth of the Great Miami River; the federal definition of the northern border was a line drawn east from the southern tip of Lake Michigan, whereas the Ohio Constitution stated the line should run from the southern tip of Lake Michigan to the most northerly cape of Maumee Bay, essentially the western tip of Lake Erie. The confusion caused by these varying descriptions of the state's borders, combined with inaccurate knowledge of geography, as no one at the time knew just how far south Lake Michigan extended, would lead to the conflict over the Toledo Strip.
November 3, 1803
The border between Tennessee and Virginia was resurveyed and established, ending the dispute over that part of the border. The border between Kentucky and Tennessee, despite following the original survey, remained vaguely defined.[41][107]
November 30, 1803
The "Southwick Jog" was transferred from Connecticut to Massachusetts, to put to rest long-standing disagreements over the border between the two states.[14] The final report of the commissioners was delivered this day;[108] it is unclear when the change formally occurred.
The acquisition expanded the United States to the whole of the Mississippi River basin,[o] but the extent of what constituted Louisiana in the south was disputed with Spain: the United States claimed the purchase included the part of West Florida west of the Perdido River, whereas Spain claimed it ended at the western border of West Florida;[p][110] and the southwestern border with New Spain was disputed, as the United States claimed the Sabine River as the border, but Spain maintained it was the Calcasieu River and others.[109]
Michigan Territory was organized from Indiana Territory, north of a line east from the southern tip of Lake Michigan, and east of a line north from the lake's northern tip.[114][115] The southeastern portion of the border technically conflicted with the definition of Ohio, which claimed the Toledo Strip north of that line; however, the exact position of Lake Michigan was not yet known.
Most of Orleans Territory was admitted as the eighteenth state, Louisiana.[r][113][122] The southeastern remainder presumably became unorganized territory, as it had no definition for a short time.
The remaining claimed portion of West Florida, west of the Pearl River, was added to Louisiana, following the assent of that state to an act passed by Congress on April 14, 1812.[126][127]
Alabama Territory created Tuskaloosa County with a description that inadvertently overlapped with Mississippi. It described the border of the county as running "a due west course to, the Tombeckbe river; thence up the same to the Cotton Gin Port".[135] Unknown at the time, the origin of the Tombigbee River and Cotton Gin Port were in Mississippi.
Alabama Territory was admitted as the twenty-second state, Alabama.[132][142] The statehood act provided for a survey of the southern part of the border with Mississippi, which was intended to be north–south, for adjustment if it was discovered to encroach upon Mississippi's established counties; it was later discovered to do so.
This is the earliest known date of the name "Arkansas Territory" being officially used instead of "Arkansaw Territory".[145]
May 12, 1820
The border between Kentucky and Tennessee was established. To make up for the fact that the border between the Cumberland Gap and the Tennessee River veered north as much as almost 10 miles from 36°30′ north, a new survey was conducted starting at that latitude on the Mississippi River and moving east to the Tennessee River, hence guaranteeing this last bit of border would fit the original ideal.[41]
July 19, 1820
The overlap of the longitudinal southern border between Alabama and Mississippi was resolved, as per the act admitting Alabama as a state, because the provisional border encroached on Mississippi.[132][146] As the result of a survey, the southern border terminus was moved about 3.8 miles to the east, which changed the border up to the then-northwest corner of Alabama's Washington County. The date when this happened is unclear; the sources available give either an unpublished report dated May 29, 1820, or the completion of the demarcation of the new line on July 19, 1820.
Change on paper only:
December 19, 1820
Alabama redefined some county borders, ending its erroneous overlap of Mississippi created on February 6, 1818.[147]
The border with the holdings of Spain was concretely defined; previously, it had been the watershed of the Mississippi River and, for Oregon Country, the Columbia River, whereas now it followed specific rivers and parallels.[v]
Florida was ceded to the United States, although the formal transfer would not happen until July.
Arkansas Territory had created Miller County south of the Red River, and this area was now on the Spanish side of the border. However, as this was a change made solely by the territory, and not by the federal government, in this map it is considered a domestic dispute.
The half of Arkansas Territory west of a line south from a point 40 miles west of Missouri's western border was returned to unorganized territory.[141][152]
January 12, 1825
A treaty with the Russian Empire established 54°40′ north as the northern border of Oregon Country for American purposes; a separate treaty created the same border between Russia and the United Kingdom.[153] As this was likely the de facto border anyway, the region is already mapped with this line.
King William I of the Netherlands, having been asked per the Treaty of Ghent to arbitrate the disputed border between Maine and the United Kingdom, rendered his decision: since reconciling the treaty with the maps given was too difficult, he drew a compromise line. The British government accepted it, but Maine protested, and on January 19, 1832, the American government rejected it.[156]
The Republic of Indian Stream recognized the jurisdiction of New Hampshire, thus ending its claimed independence. The date given is of a communication sent to British authorities;[159] other sources note a resolution passed by the citizens of Indian Stream on April 2, 1836.[157]
Wisconsin Territory was organized from the western bulk of Michigan Territory.[y][161][162] The two large peninsulas between the Great Lakes remained in Michigan Territory; the upper peninsula was included in exchange for the territory abandoning its claim to the Toledo Strip. The territory initially rejected this plan, but would accept it on December 14.
The border between New York and Vermont on the one side, and the United Kingdom on the other, was clarified by the treaty. In 1816, construction began on an unnamed fort nicknamed "Fort Blunder" on a peninsula in Lake Champlain that, while south of the surveyed border, was discovered to be north of 45° north, which was the border set by the Treaty of Paris and thus in British territory. Consequently, construction on the fort was abandoned. The Webster–Ashburton Treaty specified that section of the border was to follow the surveyed line, rather than the exact parallel, thus moving the fort's area into the United States, and a new fort, Fort Montgomery, would be built on the spot in 1844.[175] As the earlier line was surveyed, even though it did not match the definition, it was deemed to be the legitimate border.
The Republic of Texas was annexed and admitted as the twenty-eighth state, Texas, extending the United States southwest to the Rio Grande.[178][179] All of Texas was claimed by Mexico. While many sources state that Mexico recognized the independence of the eastern portion of Texas, the treaties were rejected by the Mexican government. Texas formally handed over sovereignty to the United States in a ceremony on February 19, 1846.[180] The annexation led to the beginning of the Mexican–American War a few months later.[180]
The treaty was vague on which strait should be the border between Vancouver Island and the continent, thus causing a dispute over ownership of the San Juan Islands.[182] It specified "through the middle of the said channel and of Fuca Straits, to the Pacific Ocean".
Northwestern North America:
Disputes:
September 22, 1846
Following the capture on August 18, 1846, of Santa Fe, the capital of the Mexican territory of Santa Fe de Nuevo México,[183] a code of laws known as the Kearny Code was created for the area.[184][185] The region overlapped with Texas' claim, though Texas had little to no control over the area outside of its eastern quarter.
Unofficial change:
December 28, 1846
The portion of Iowa Territory south of 43°30′ north and east of the Big Sioux River was admitted as the twenty-ninth state, Iowa. The remainder became unorganized territory.[168][186]
The southern bulk of Wisconsin Territory was admitted as the thirtieth state, Wisconsin.[ab] The remainder became unorganized territory.[162][190] However, the citizens of the remainder decided to continue on with a civil government, and even elected a delegate to the United States House of Representatives who would be seated on January 15, 1849, essentially making this region a de facto continuation of Wisconsin Territory.[191]
A local government formed the State of Deseret and claimed a vast portion of the southwest, including most of the Mexican Cession. Though it petitioned to be admitted to the United States, the proposal was rejected and, in 1850, Utah Territory was formed instead.[198] The claimed area overlapped slightly with Texas' claimed area, as well as part of Oregon Territory.
The western portion of the Mexican Cession was admitted as the thirty-first state, California.[ad][3][203] The portion of the remainder north of 37° north and west of the summit of the Rocky Mountains was organized as Utah Territory.[204][205] Part of Utah Territory overlapped with the portion of Texas that would be purchased on December 13, 1850, but the law authorizing the purchase was passed on this day, so the borders of Utah Territory assumed that the purchase would go through.
December 9, 1850
The United Kingdom ceded less than one acre of underwater rock for a lighthouse in Lake Erie near Buffalo, New York; although it was on Middle Reef, it was named for the nearby Horseshoe Reef.[206] It was surrounded by British waters, thus creating a form of enclave.[207]
A small strip between the Texas Panhandle and Kansas Territory was unclaimed because it fell south of Kansas Territory's border but north of 36°30′ north, which had been established in the Missouri Compromise as the northern limit of slavery, and thus Texas could not have it. This became known as the Public Land Strip, or sometimes "No Man's Land".[216]
June 30, 1854
The United States purchased a large parcel from Mexico known as the Gadsden Purchase, as it offered a much better route for a southern transcontinental railroad.[ag][217][218] This resolved the border dispute, since the disputed land was included in the purchase.[192]
A team of surveyors created the "Middleton Offset", a small notch in the border between Kentucky and Tennessee. It is unknown exactly why this was done, though one theory is a local landowner wanted his property in Tennessee.[226][227]
Texas created Greer County, claiming part of Indian Territory based on a different understanding from the federal government of which fork of the Red River was the border between the two.[230]
Mississippi proclaimed its secession from the Union, withdrawing from Congress.[232]
Disputes:
January 10, 1861
Florida proclaimed its secession from the Union, withdrawing from Congress.[232]
Disputes:
January 11, 1861
Alabama proclaimed its secession from the Union, withdrawing from Congress.[232]
Disputes:
January 19, 1861
Georgia proclaimed its secession from the Union, withdrawing from Congress.[232]
Disputes:
January 26, 1861
Louisiana proclaimed its secession from the Union, withdrawing from Congress.[232] However, the 1st and 2nd congressional districts, around New Orleans, maintained representation in Congress.
North Carolina proclaimed its secession from the Union, withdrawing from Congress.[232]
Disputes:
May 21, 1861
North Carolina was admitted to the Confederate States. The law admitting the state required a presidential proclamation before it was to take effect,[245] which sources say took place on this date;[246] the only primary source found so far is a statement from Jefferson Davis on July 20 stating that the proclamation had been made.[247]
Tennessee proclaimed its secession from the Union, withdrawing from Congress.[232] However, the 2nd, 3rd, and 4th congressional districts in the central part of the state maintained representation in Congress.
Following the Confederate occupation of Columbus, Kentucky, on September 3, 1861, the state abandoned neutrality and aligned with the Union government.[251]
no change to map
October 31, 1861
A splinter government in Neosho, Missouri, proclaimed the secession of the state from the United States.[232]
The splinter Neosho government of Missouri was admitted to the Confederate States. The Confederate States never held much power over the state, but it was given full representation in the legislature.[252]
Wyoming Territory was organized from portions of Dakota, Idaho, and Utah Territories.[ar][289][288] The territory would remain under the jurisdiction of the Dakota Territory until its own government was organized on May 19, 1869.[290] The act organizing Wyoming Territory became law on this date, but it is unclear if the territory could be considered "organized" until May 19, 1869, as the act specifies it was not to take effect until a government is organized; however, all sources use this date as the creation, and most use it for the organization, of the territory. A tiny portion of the Dakota Territory was erroneously left behind on the western side of Wyoming Territory.[291]
August 12, 1868
The list of bonded guano island claims mentions "Islands in Caribbean Sea not named" bonded on this date, but it is unknown to what this is referring.[4]
Western Triangle Island, claimed by Mexico, was claimed by the United States under the Guano Islands Act.[4] The list of bonded claims also mentions a "De Anes" island claimed on this date, with coordinates matching Isla de Aves; however, the same list points out that the claim to "Aves Island" was found to be invalid.
The Gilbert Islands became a protectorate of the United Kingdom, thus initiating a claim on Butaritari and Marakei.[270] No record of a United States claim exists after this point, so it is assumed this is when the claim fell dormant.
The Republic of Hawaii was annexed.[319] The ceremony to transfer sovereignty occurred on this date; the act was signed on July 7, 1898.[320]Johnston Atoll was not included with Hawaii, nor was Sikaiana Atoll, which had been ceded to Hawaii in 1856 by its residents and approved by King Kamehameha IV. However, the annexation was based on the islands named in a report of the Hawaiian Commission, which omitted Sikaiana.[321][322]
The newly acquired Samoan islands were established as Naval Station, Tutuila. It included all of the islands granted by the Tripartite Convention, though formal cession of the islands by local authorities would take place later in 1900 and 1904.[326]
The transfer for a thin sliver of Bristol, Tennessee, to Bristol, Virginia, was approved by Congress after having been approved by both states.[331][332] The location of the border along Main Street (now State Street) between the two cities was either the northern sidewalk of the street, or down the middle of the street; Tennessee's cession of the northern half of the street laid the issue to rest.
On this same date several islands, Cagayan de Sulu and Sibutu among them, were purchased from Spain and assigned to the Philippines, which was then being governed as a U.S. insular area. The borders specified in the Treaty of Paris of 1898 had excluded these islands; the new treaty simply ceded "any and all islands belonging to the Philippine Archipelago".[333][334]
Land along southern Guantánamo Bay was leased in perpetuity from Cuba for use as a naval base;[338] the treaty took effect February 23, 1903, and the formal handover occurred on this date.[339]
no change to map
May 4, 1904
The United States took ownership of the Panama Canal Zone. At this stage, only the most basic borders were defined; it was a zone surrounding the canal on each side for five miles, but excluded the cities of Colón and Panama City, which remained exclaves of Panama, as well as the water for their harbors.[340] The Hay–Bunau-Varilla Treaty granting it to the United States was ratified on February 26, 1904.[341] A formal border agreement, which also gave the Canal Zone some land and a lighthouse in northwest Colón, would be ratified on June 15, 1904.[342][343]
The "Taft Agreement" was made with Panama on December 3, with one of its sections refining the maritime boundary of the harbor of Panama City and the Panama Canal Zone.[344][345] It became effective December 12.
A boundary treaty with the United Kingdom on behalf of Canada redefined the maritime borders between the United States and Canada.[350] Among other changes, this "de-enclaved" Horseshoe Reef Lighthouse in Lake Erie by making the water around it contiguous with the water on the American side of the border.[207][351]
A boundary treaty with the United Kingdom on behalf of Canada addressed a slight uncertainty in the maritime border in Passamaquoddy Bay between Maine and Canada.[353][354][355] The border was adjusted to run east of Pope's Folly Island, which previously lay on the border line, and had been the subject of some debate for many years.[356][357]
The Corn Islands were leased from Nicaragua for a period of 99 years; however, this was not a full transfer of sovereignty, and the islands were never administered as an insular area.[363]
no change to map
May 1, 1915
The borders of the Panama Canal Zone were explicitly defined. Whereas the original definition was a simple corridor surrounding the canal, this treaty specified the actual border. Among the changes this caused were: a slice of Canal Zone was ceded to Panama so Panama City would be connected with the rest of the country; the middle island of the Las Tres Hermanas Islands, which marked the border of Panama City's harbor, was wholly made part of Canal Zone; Gatun Lake and other surrounding waters were formally annexed to the territory; and an area of northwest Colón was ceded to Canal Zone.[364][365][366]
The "Wedge" dispute between Delaware and Pennsylvania was resolved in Delaware's favor. The disputed land had generally been administered by Delaware, even electing a member of the Delaware legislature in the mid-19th century,[379] but federal maps had included the land as part of Pennsylvania at least as late as 1900.[380] The states had agreed on a resolution, and it was affirmed by an act of Congress on this date.[381][382] Some sources, both contemporary and modern, note that, in the original process of resurveying the border in 1892, a very thin, horn-shaped region along the arc was transferred from Delaware to Pennsylvania;[379][382][383] however, no federal maps found reflect this, and it is unclear if this transfer actually occurred.
The border with Canada was adjusted in several places.[389][390] The only change to a land border redefined how the border between the Lake of the Woods and the Rocky Mountains should be considered; previously, the border followed the curve of the parallel between each border monument, while the treaty changed this to straight lines between each monument. Through this, the United States netted a gain of between 30 and 35 acres of land. Because of the extremely small shift, the lack of specific documentation of where the changes occurred, and the lack of any human impact, this change is not mapped. There was also a change to the border in the Lake of the Woods; a surveying anomaly caused the previous border to intersect itself several times in the lake, creating enclaves of United States water surrounded by Canadian water. The treaty changed the border to use the southernmost intersection as the northwestern point of the Lake of the Woods. Finally, the maritime border in the Bay of Fundy was adjusted, netting Canada roughly 9 acres of water.
Johnston Atoll was established as a federal bird refuge and placed under the jurisdiction of the United States Department of Agriculture.[391] The atoll had originally been claimed by both the United States and Hawaii in 1858, but little activity apart from guano mining had taken place, and it had been largely abandoned for decades.[228]
no change to map
November 22, 1926
The Supreme Court of the United States defined the border between Michigan and Wisconsin, transferring all islands south of the Quinnesec Falls on the Menominee River to Wisconsin, and all islands north of the falls to Michigan; it is unknown specifically which islands were transferred in this fashion. However, an error in the border description introduced a small overlap between the two states over several islands in Lake Michigan north of the Door Peninsula.[392]
July 18, 1927
The United States expropriated from Panama another 33 hectares of land on the islands of Taboga and Taboguilla and annexed them to the Panama Canal Zone.[367]
The United States expropriated from Panama three hectares of land at El Cerro de Doscientos Pies ("200-Foot Hill") near Las Minas Bay and annexed it to the Panama Canal Zone.[367][375]
too small to map
July 22, 1930
The United States expropriated from Panama 25 hectares on Jicarita Island and 60 hectares at Punta Morro de Puercos and annexed them to the Panama Canal Zone.[367]
The United States adjusted the border at Punta Paitilla in the Canal Zone, returning a small amount of land to Panama. This was the site for a planned new American embassy, which had to be built on foreign soil.[396]
The Mangsee Islands and seven of the Turtle Islands were ceded by the United Kingdom from North Borneo to the Philippines. The islands were supposed to be included in the 1900 transfer of islands from Spain to the United States. Per the terms of the treaty, the United Kingdom continued to administer the islands until requested, and, after the Philippines' independence, the Philippine government made such a request and took control.[398]
A treaty created the Rio Grande Rectification Project, which, from 1935 to 1938, straightened and stabilized the path of the Rio Grande through the El Paso–Juárez Valley. By the end of the project, 174 parcels had been transferred between Mexico and Texas, each side receiving an equal area of land.[399][400]
Panama gained a sovereign corridor that was carved out of the Panama Canal Zone connecting Colón with the rest of Panama, along with a three-dimensional "tube" of sovereignty for a future crossing over an American highway. A corridor consisting of the road from the Canal Zone boundary to Madden Dam was annexed to the Canal Zone.[407]
The Second Philippine Republic, in exile in Tokyo since April 3, 1945, was dissolved. The process of re-establishing the Commonwealth government on Philippine soil had started on October 23, 1944.[411]
Panama's corridor connecting Colón with the rest of Panama was realigned within the Panama Canal Zone. Several three-dimensional "tubes" of sovereignty were also created, allowing Panamanian bridges to pass over rivers and a highway at several locations within the Canal Zone.[419][420]
Several parcels were exchanged between Texas and Mexico along the Rio Grande in areas near Presidio and Hidalgo, Texas,[428] including the Horcón Tract, on which the town of Río Rico was located,[429] and Beaver Island near Roma, Texas. In addition, Mexico ceded 823 acres (3.33 km2) to the U.S., while the U.S. ceded 2,177 acres (8.81 km2) to Mexico, primarily to straighten sections of the Rio Grande for flood control.[430]
December 16, 1977
A treaty defining the maritime border with Cuba was signed; though it has never been ratified by the United States Senate, it is provisionally enforced by agreement renewed every two years.[355]
The Panama Canal Zone was ceded to Panama. The United States and Panama continued to share operational control of the canal until December 31, 1999, when it would be fully turned over to Panama.[433] The United States retained control over several hundred specified areas to be turned over in piecemeal fashion over the years.
Caribbean Sea:
November 24, 1980
The maritime border between the United States and Venezuela was defined.[355][434]
no change to map
September 17, 1981
The United States recognized the sovereignty of Colombia over Roncador Bank and Serrana Bank, and the claim on Quita Sueño Bank was abandoned by the United States, as it was no longer above the seas at high tide, and thus the government considered it unclaimable.[363][435]
The International Court of Justice made its judgment on where the maritime border should be in the Gulf of Maine between the United States and Canada.[440][355] No land changed hands. The scope of the case did not include the sovereignty of Machias Seal Island, but the judgment enabled defining the extent of the disputed water area around that island (an area of 210 square nautical miles).[427]
The maritime border between the United States and the Soviet Union was provisionally defined.[443][355] The two countries agreed on this date to abide by the terms of the treaty pending its ratification and entry into force,[444] but while it was ratified by the United States Senate on September 16, 1991,[445] it was never ratified by the Soviet Union or its successor state, Russia.
The maritime border between the United States and Mexico was defined.[355][451]
May 26, 1998
The Supreme Courtruled that extra land added to Ellis Island since the original island was officially granted to New York in an interstate compact with New Jersey in 1834 belonged to New Jersey, because the island was within the territorial waters of New Jersey. The original natural boundary of Ellis Island remained an enclave of New York.[452]
December 31, 1999
All former Panama Canal Zone parcels not turned over since 1979, as well as all joint canal operations areas, were transferred to Panama.
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January 17, 2001
The maritime border between the United States and Mexico on the continental shelf in the western Gulf of Mexico beyond 200 nautical miles was defined.[355][453]
no change to map
November 24, 2009
Six islands along the Rio Grande were ceded from Texas to Mexico, and three islands and two bancos were ceded from Mexico to Texas. The transfer, which had been pending for 20 years, was the first application of Article III of the 1970 Boundary Treaty.[355][394][454]
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September 23, 2014
The maritime border between the United States and Niue was defined.[355][455] The treaty was signed on May 13, 1997, but it was not ratified by the United States until at least 2002, and the United Nations shows it as entering into force on this date.[456]
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January 1, 2017
The border between North Carolina and South Carolina was clarified following years of surveys and negotiation, moving 19 homes across state lines.[457][458]
An example of a banco, created when a meander is cut off by a new, shorter channel, leaving a cut-off section of land surrounded by a U-shaped (oxbow) lake
The Banco Convention of 1905 between the United States and Mexico allowed, in the event of sudden changes in the course of the Rio Grande (as by flooding), for the border to be altered to follow the new course.[461] The sudden changes often created bancos (land surrounded by bends in the river that became segregated from either country by a cutoff, often due to rapid accretion or avulsion of the alluvial channel), especially in the Lower Rio Grande Valley. When these bancos are created, the International Boundary and Water Commission investigates if land previously belonging to the United States or Mexico is to be considered on the other side of the border.[462] In all cases of these adjustments along the Rio Grande under the 1905 convention, which occurred on 37 different dates from 1910 to 1976, the transferred land was minuscule (ranging from one to 646 acres) and uninhabited.[463][464][465]
^The borders of the country followed the colonial borders; for simplicity, the maps use the borders defined in the 1783 Treaty of Paris. The only substantive difference between the borders before and after the Treaty of Paris is the southwest border: when Great Britain had ownership over West Florida, they had moved its border north, to a line east from the mouth of the Yazoo River, and that area thus did not belong to Georgia; the treaty granted the area between this and 31° north to the United States.
^The New York towns petitioning to join Vermont were: "Black-Creek" (unknown; possibly is or is near Hebron), Cambridge, Fort Edward, Granville, "Greenfield" (unknown; there is a town named Greenfield but it lies west of the Hudson River, which was explicitly the western extent of the West Union), Hoosick, Kingsbury, "Little Hoosack" (unknown; presumably near Hoosick), Saratoga, "Scorticook" (possibly Schaghticoke), Skeensborough (now Whitehall), and "Upper-White-Creek" (probably White Creek).[44] The specific extent of the towns annexed is unknown, as township borders were often delineated only when a dispute arose; the map uses the common interpretation.
^The treaty established the boundaries of the new country, from the Bay of Fundy: up the "St. Croix River" (which river this referred to was disputed) to its source; north to the height of the land (the "Northwest Angle of Nova Scotia"); along the height of the land to the "northwesternmost Head" of the Connecticut River (which source this referred to was disputed); down that to 45° north; west to the St. Lawrence River; up that to the Great Lakes, through Lake Ontario, the Niagara River, Lake Erie, the Detroit River, Lake St. Clair, the St. Clair River, Lake Huron, and Lake Superior; to "Long Lake" (which lake this referred to was disputed) towards the Lake of the Woods; to the northwest angle of the Lake of the Woods; then west to the Mississippi River. However, the Lake of the Woods was north of the source of the Mississippi River; maps universally show this undefined border as a straight line, nearly straight south, between the two points. From there, it followed the Mississippi River down to 31° north; east to the Chattahoochee River; down that to the confluence of the Chattahoochee and Flint rivers; a line from there to the source of the St. Mary's River; then down that to the Atlantic Ocean.[53]
^There is disagreement over if the state was named Franklin or Frankland; sources tend to refer to Franklin as the specific state, and Frankland as the region.[55]
^Massachusetts's ceded claim was a strip of land west of New York and Pennsylvania stretching to the Mississippi River, bounded by the latitudes of Massachusetts Bay Colony's original charter: on the north by a line west from one league north of Lake Winnipesaukee, and on the south by a line west from Massachusetts' southwest corner.[47]
^Connecticut's ceded claim was a strip of land west of 120 miles west of Pennsylvania (the western border of its Western Reserve) stretching to the Mississippi River, bounded by 41° north and the southern edge of Massachusetts's western claim, roughly 42°2′ north.[47]
^Massachusetts's ceded claim was the portion of New York 82 miles west of where the Delaware River left New York, to an unclear western boundary, with one source saying it was as far as one mile east of the Niagara River.[47]
^The new North Carolina–federal border was, from the north, southwest along various ridges of the Great Smoky Mountains; however, issues caused surveyors to eventually run a line roughly due south rather than continue along the ridge.[19]
^The new New York–Vermont border was, from the north: Lake Champlain, the Poultney River, then south following borders of townships.[32]
^The new Indiana Territory–Northwest Territory border was, from the south, a line from the mouth of the Kentucky River to Fort Recovery, then north.[101]
^The new Georgia–federal border was, from the south, up the Chattahoochee River to its great bend (near West Point), then a line from there towards and past Nickajack. The border's description said it would go until it reached the Tennessee River, and follow that up the river to Tennessee, but the river lay entirely within Tennessee.[12]
^There was some question as to whether the purchase also included the basins of the Missouri River and the Red River of the North, but the question was not relevant before the Treaty of 1818 definitively settled the border. Maps universally show the purchase including the Missouri River basin but excluding the Red River basin.[109]
^The new Illinois Territory–Indiana Territory border was, from the south, the Wabash River up to Post Vincennes, then north.[117]
^The northwestern remainder of Orleans Territory presumably rejoined Louisiana Territory, as its extent was still vaguely defined.
^Indiana was defined as the territory north of the Ohio River and east of the Wabash River, but while the territory's line turned north at Post Vincennes, the state's border continued up the Wabash until it reached the point where a line drawn north from Post Vincennes would last intersect the river as it weaved back and forth. The northern border of the state was a line east from 10 miles north of the southern tip of Lake Michigan, until it reached the meridian that formed Ohio's western border, which was a line drawn north from the mouth of the Great Miami River.[101]
^The new Arkansas Territory–federal border, from the north, a line from the southwestern corner of Missouri to a point on the Arkansas River "100 paces east" of Fort Smith, as the border of the lands of the Eastern Choctaw, then south.[141] However, the Arkansas Supreme Court determined in 1909 that the "100 paces east" was a clerical error, and that logically it should have said "100 paces west".[154]
^The new Michigan Territory–Wisconsin Territory border was, from Lake Superior: up the Montreal River to Lac Vieux Desert; a line to the source of the Menominee River; then down that to Green Bay. However, this definition was impossible: The Montreal River ended long before it reached Lac Vieux Desert. The issue would be resolved in 1850.[115]
^The new northeastern border was, from Passamaquoddy Bay: up the St. Croix River to its source; north to the St. John River; up that to the St. Francis River; up that to its source outlet at Lake Pohenegamook; southwest to the northwest branch of the St. John River; a line from there to where the St. John River crosses 46°25’ north; up the river to its source; along the highlands to the source of Halls Stream, then down that to 45° north.[144][15]
^The new international border was, from the Rio Grande: along the southern and western border of New Mexico until it meets the Gila River; down that to the Colorado River; then a line to a point one league south of the port of San Diego. However, the southern border of New Mexico was in question, with the US claim being 31°52′ north, and the Mexican claim being 32°22′ north.[192]
^The new California–federal border was, from the north: south along 120° west to 39° north; a line to where the Colorado River intersects 35° north; then down the Colorado River.[3]
^The new New Mexico Territory–federal border was, from 36°30′ north and 103° west: north to 38° north; then west to the summit of the San Juan Mountains (called then the Sierra Madre).[208]
^The new international border was, starting from where the Rio Grande crosses 31°47′ north: west 100 miles; south to 31°20′ north; west to 111° west; a line to a point on the Colorado River 20 miles below the mouth of the Gila River; then up the Colorado River.[217]
^The decree transferred land from the left bank of the Blackstone River to Rhode Island, including what is now East Providence, in exchange land around Fall River being transferred to Massachusetts.[14]
^The borders of the Department of Alaska were, from the Dixon Entrance: Up the Portland Channel to 56° north; then along the "summit of the mountains situated parallel to the coast" (the definition of which was disputed) to 141° west; then north.[279]
^The new Oklahoma Territory–federal border was, from where the Red River meets 98° west: north to the Canadian River; down that to Seminole land; north along that border to the North Canadian River; down that to Creek land; north and east along that border to 96° west; then north. This omits the Cherokee Outlet, whose complex borders separated the main portion of Oklahoma Territory from the former Public Land Strip.[312]
^"Articles of Confederation". The Avalon Project at Yale Law School. Archived from the original on October 29, 2015. Retrieved October 31, 2015.
^ abVermont State Papers, pp. 136–137: "Agreeably to the recommendation of the committees, the Legislature of Vermont was adjourned to the first Wednesday of April [1781]; at which time, it met at Windsor, and the union of the grants, east and west of Connecticut river, was consummated"
^ abTreaty of Paris, 1783; International Treaties and Related Records, 1778–1974; General Records of the United States Government, Record Group 11; National Archives.
^Northwest Ordinance, July 13, 1787; (National Archives Microfilm Publication M332, roll 9); Miscellaneous Papers of the Continental Congress, 1774–1789; Records of the Continental and Confederation Congresses and the Constitutional Convention, 1774–1789, Record Group 360; National Archives.
^Tindall, William (February 25, 1919). "Naming the Seat of Government of the United States: A Legislative Paradox". Records of the Columbia Historical Society. 23. Historical Society of Washington, D.C.: 10–25. JSTOR40067136.
^Carter II, Edward C. (1971–1972), "Benjamin Henry Latrobe and the Growth and Development of Washington, 1798–1818", Records of the Columbia Historical Society: 139
^Text from Webster–Ashburton Treaty: "till the line thus run intersects the old line of boundary surveyed and marked by Valentine and Collins previously to the year 1774, as the 45th degree of north latitude, and which has been known and understood to be the line of actual division between the States of New York and Vermont on one side, and the British Province of Canada on the other"
^Williams, J. Fletcher (1894). Henry Hastings Sibley: A Memoir. Minnesota Historical Society. pp. 277–281. Archived from the original on March 7, 2016. Retrieved December 28, 2015.
^Danver, Steven L (April 25, 2013). "Young, Brigham". Encyclopedia of Politics of the American West. p. 675. ISBN978-1-4522-7606-9. Retrieved January 28, 2016.
^Kenneth R. Turner, "No Man's Land", Archived April 2, 2015, at the Wayback Machine Encyclopedia of Oklahoma History and Culture, www.okhistory.org (accessed June 4, 2015).
^Act authorizing readmission on ratification of 14th amendment: 15 Stat.73. Florida ratified the amendment before that law was passed, so Florida was readmitted upon passage of the law.
^Act authorizing readmission on ratification of 14th amendment: 15 Stat.73. Proclamation of North Carolina's ratification: 15 Stat.703.
^Act authorizing readmission on ratification of 14th amendment: 15 Stat.73. Proclamations of Louisiana's and South Carolina's ratification: 15 Stat.704.
^Act authorizing readmission on ratification of 14th amendment: 15 Stat.73. Proclamation of Alabama's ratification: 15 Stat.704.
^Watkins, Albert (1913). "Nebraska Territorial Acquisition". Collections of the Nebraska State Historical Society. XVII. Nebraska State Historical Society: 53. Retrieved May 18, 2015.
^"The Panama Canal Record". Vol. XIII, no. 39. Balboa Heights, Canal Zone: The Panama Canal. May 12, 1920. pp. 584–585. ... it was not until the year 1918, when the Governor of the Canal Zone addressed a communication to the Secretary of Foreign Affairs of the Republic of Panama stating that the United States Government would require 50.6 hectares, that the exact area expropriated was definitely known.
^Canal Zone. Office of the Governor. (1919). Annual Report of the Governor of the Panama Canal for the Fiscal Year ended June 30, 1919. Washington, DC: U.S. Government Printing Office. p. 94. Archived from the original on May 6, 2016. A survey was made and a map drawn up showing the boundary lines of the Punta Paitilla military reservation. Various areas were determined with reference to high and low water and the old and new city boundary lines. Permanent monuments were set and a description written up by metes and bounds. A tracing was made of the map of the military reservation known as area 'A'.
^Link to a download for the United States Geological Survey map of the Elkton Quadrangle from August 1900: [2]. Note that later reprints of the same map, as early as 1906, changed ownership of the Wedge to Delaware: [3]
^Metz, Leon C. (June 12, 2010). "Bancos of the Rio Grande". Handbook of Texas Online. Texas State Historical Association. Archived from the original on October 27, 2016. Retrieved July 13, 2015.
