HISTORY23 - Territorial Growth of the United States

This article is a history timeline of U.S. territorial growth. It starts with the formation of the United States of America in 1783, continues through the completion of today’s contiguous U.S., covers the acquisition of lands for our 49th and 50th states, Alaska and Hawaii, and ends with a discussion of populated American territories.

This article is a follow-on to my recent blogs on history of the Spanish Empire in North America, and as we shall see, there is a direct connection with the history of the growth of U.S. territory. 

The map below identifies all major land acquisitions that built up the contiguous United States and will be discussed below.

1783 - United States of America

Great Britain had established settlements at Jamestown in 1607 and at Plymouth in 1622, and from there expanded along the Atlantic Coast to 13 colonies, stretching from New Hampshire and Massachusetts in the north to Georgia in the south, by 1775, at the start of the American Revolution (1775-1783). 

France started colonization in North America along the St. Lawrence River in the early 1600s, exploring to the north in today’s southern Canada, and to the south and west, claiming land west of the Mississippi River and lands in today’s American mid-west, easing up to the Appalachian Mountains against England’s colonies. In 1762, France lost the Seven Years War to the British, and ceded its territory in Canada and east of the Mississippi to Great Britain, as well as ceding French Louisiana west of the Mississippi River, to Spain, an ally during the War. 

The treaty of Paris, signed on September 3, 1783, ended the American Revolutionary War with Great Britain. The treaty set the boundaries between the British Empire in North America and the United States of America, consisting of thirteen colonies that had become free, sovereign, and independent states. 

The treaty negotiations were very favorable to the United States. The British saw a chance to split the U.S. away from its ally France and make the new country a valuable economic partner for the future. The terms were that the U.S. would gain all the land east of the Mississippi River, north of Florida, and south of today’s Canada. The northern boundary would be almost the same as today. 

Total area of the new United States was about 800,000 square miles (27%). Note: The parenthetical number following the area of this first increment of U.S. territory [and for those major land acquisitions that followed] is the approximate percentage of the eventual total area of the contiguous United States, that would be completed by 1853. 

Maine was a part of Massachusetts at this time and its northern border was disputed with Britain. Vermont was included within the American boundaries because the state of New York insisted that Vermont was part of New York, although Vermont was then under a government (Vermont Republic) that considered Vermont not to be a part of the United States. 

In a separate treaty with America’s second ally, Spain, Great Britain ceded Florida to Spain. During the British ownership of West Florida, the British had moved its border north, leaving the ownership of a chunk of West Florida in dispute.

By 1783, some of the original 13 states, particularly Virginia, North Carolina, and Georgia, had made claims of land ownership to the west of the Appalachian Mountains all the way to the Mississippi River. These claims, and others, would be resolved in the next few years, mostly producing new American states. For the present, the northwest part of the new American lands remained “unorganized,” not within the bounds of a U.S. state. 

The 13 original colonies became the cornerstones of the new United States of America in 1783.
The light-blue territory represents land claimed by multiple states.

1803 - Louisiana Purchase 

With the acquisition of Louisiana in 1762, and Florida in 1783, the Spanish Empire in North America reached it greatest extent; Spain’s territory completely encircled the Gulf of Mexico and stretched from Florida, west to the Pacific Ocean, and north to today’s Canada, west of the Mississippi River. 

Spanish Louisiana encompassed the western basin of the Mississippi River plus the city of New Orleans. The territory extended slightly north into today’s Canada and did not include Rupert Land, containing the Hudson Bay drainage basin - border issues that would be resolved in 1818 (see below). 

Spain ceded Louisiana back to France in 1801 in exchange for territories in Tuscany, Italy, and in 1803, France, desperate for funds to pursue European interests, sold the territory of 828,000 square miles (28%) to the U.S. for $15 million in the Louisiana Purchase - doubling the size of the U.S. at a price of less than three cents per acre. 

Louisiana’s border with Florida was disputed with Spain. The U.S. claimed that the purchase included all of West Florida, while the Spanish claimed that it did not. This issue wouldn’t be settled until 1819 (see below). 

The Louisiana territory was renamed the Missouri territory in 1812 to avoid confusion with the new state of Louisiana, which had been admitted to the Union earlier that year. 

The Louisiana Purchase of 1803 doubled the size of the United States.

1810, 1812 - Annexation of West Florida 

Believing that it was part of the Louisiana Purchase, U.S. President James Madison ordered the disputed territory in West Florida to be occupied by U.S. troops and annexed it in two pieces as United States territory, without agreement from the Spanish who maintained their claim on the land. See the map above. 

1818 - Northern Border Adjustments 

The Treaty of 1818 between the United States and the United Kingdom resolved northcentral boundary issues. 

The two nations agreed to a 49th parallel north boundary line, east of the Oregon Country, in part because a straight-line boundary would be easier to survey than the pre-existing boundaries based on watersheds. The treaty marked both the United Kingdom's last permanent major loss of territory in what is now the Continental United States and the United States' only permanent significant cession of North American territory to a foreign power. 

The British ceded all of the so-called Rupert's Land, south of the 49th parallel, east of the Continental Divide, covering the northern parts of today’s North Dakota and Minnesota. The United States ceded the northernmost edge of the Missouri Territory, north of the 49th parallel and north of today’s state of Montana. See the map above. 

The treaty also allowed for joint occupation and settlement of the Oregon Country to the west. 

1819 - United States-New Spain Boundary Settlement 

In the early 1800s, Florida became an economic burden to Spain, which could not afford to send settlers or garrisons to protect the area against native Seminole raiding or American settler encroachment, so in 1819, the Spanish government agreed to cede all of Florida to the U.S., ending the long-standing West Florida land dispute, and adding 85,000 square miles (3%) to U.S. territory, in exchange for settling a boundary dispute in the southwest Missouri Territory (today’s Texas): Spain ceded land east of the Sabine River and the U.S. gave up claims to two parcels of land in the Missouri Territory, south of the Red River, and south of the Arkansas River (a substantial part of today’s Texas). Spain also ceded a small parcel of land in today’s northern Colorado. 

The Adam-Onís Treaty formalized the agreement between the United States and Spain in 1819, signed in 1821, that ceded Florida to the U.S. and defined the boundary between the U.S. and New Spain. Spain gave up its claims to the Oregon Country, and the Treaty set the northern boundary of New Spain along the Sabine, Red, and Arkansas Rivers to the Rocky Mountains, then west along the 42nd parallel to the Pacific Ocean. 

The Adams-Onis Treaty ceded Florida to the U.S. and set the boundary between the U.S. and New Spain, Spanish territory in North America

The Treaty remained in effect for only 183 days, from February 22, 1821 to August 24, 1821, when Spanish military officials signed the Treaty of Cordoba, acknowledging the independence of Mexico, and relinquishing all New Spain lands in North America to Mexico. 

While Mexico was not initially a party to the Adams-Onis Treaty, in 1831, Mexico agreed to the terms of the Treaty. 

1842 - Adjustments to Maine, Minnesota Borders 

The Webster-Ashburton Treaty of 1842 settled two northeastern border disputes with the United Kingdom. Along the Maine border, the U.S gained 7,000 square miles of the disputed territory, but ceded the northern 5,000 square miles to the United Kingdom. In addition, the United States received 6,500 square miles of land along the Minnesota-United Kingdom border. See the first map in this article. 

1845 - Texas Annexation 

In 1819, the Adams-Onís treaty set the southeastern boundary between Spanish Texas and American Louisiana at the current border between the U.S. states of Texas and Louisiana. Eager for new land, many settlers from the U.S., refused to recognize the agreement and crossed into Spanish Texas to make a new life there. This continued as Mexico gained its independence from Spain in 1821 and transitioned from a Spanish territory to an independent country. By 1834, American settlers in Mexican Texas outnumbered Mexican settlers by a considerable margin. 

Fearing open rebellion of their Anglo subjects, Mexican authorities began to step up military presence in Texas. American leadership in Texas began to organize its own military, and hostilities broke out in late 1835, with the Battle of Gonzales, the first engagement of the Texas Revolution. On March 2, 1836, during the Battle of the Alamo, the Americans (called Texians) declared independence from Mexico, establishing the Republic of Texas. Seven weeks later, Texian forces defeated Mexican forces at the Battle of San Jacinto in the decisive battle of the Revolution. Although too weak to continue to fight the Texians, Mexico refused to recognize Texas’ independence. 

The huge Republic of Texas (former Mexican state of Coahuila y Tejas) was bordered by Mexico to the west and southwest, the Gulf of Mexico to the southeast, the two U.S. states of Louisiana and Arkansas to the east, and parts of the current U.S. states of Oklahoma, Kansas, Colorado, Wyoming, and New Mexico. The Republic’s southern and western boundaries with Mexico were disputed throughout the Republic’s existence by Mexico. 

The Republic of Texas lasted about ten years, under sporadic attack from Mexican forces and multiple raids from Comanche Indians, from their Comanchería base in central Texas. 

Texas, including the disputed territories, a total area of 389,000 square miles (13%), was annexed by the United States on December 29, 1845, and immediately admitted to the Union as the 28th state, extending the U.S. southwest to the Rio Grande River. This annexation led to the beginning of the Mexican-American war a few months later. 

In 1845, the United States annexed the Republic of Texas, including disputed lands.

1846 - Oregon Country 

The Treaty of 1818 between the United States and Great Britain had provided for joint control of the Oregon Country, but joint control steadily became less tolerable by both sides. American expansionists called for the annexation of the entire region, up to parallel 54 degrees, 40 minutes north, the southern limit of Russian America. 

After the outbreak of the Mexican-American War in April 1846 (see below), with U.S. attention and military resources diverted, a compromise was reached in the Oregon Treaty between the Great Britain and the United States that was signed on June 15, 1846 to establish the U.S.-Britain boundary at the 49th parallel north. Vancouver Island was an exception and retained in its entirety by the British. 

A total of 285,000 square miles (10%) was added to U.S. territory. 

The addition of Oregon Country completed the northwest border of continuous America.

1848 - Mexican Cession 

In the 1844 United States presidential election, James K. Polk was elected on a manifest destiny platform of expanding U.S. territory in Oregon and Texas. (Manifest destiny was the 19th-century doctrine or belief that the expansion of the U.S. throughout the American continent was both justified and inevitable.) 

Polk advocated expansion by either peaceful means or by armed force, with the 1845 annexation of Texas, which Mexico never did recognize, as furthering that goal. For Mexico, this was itself a provocation, but Polk went further, sending U.S. Army troops to the area; he also sent a diplomatic mission to Mexico to try to negotiate sale of territory. U.S. troops' presence was provocative and designed to lure Mexico into starting a conflict, putting the onus on Mexico and allowing Polk to argue to Congress that a declaration of war should be issued. Mexican forces attacked U.S. forces, and the United States Congress declared war on April 25. 1846. 

Beyond the disputed area of Texas, U.S. forces quickly occupied the regional capital of Santa Fe de Nuevo México, along the upper Rio Grande, which had trade relations with the U.S. via the Santa Fe Trail between Missouri and New Mexico. U.S. forces also moved against the Spanish province of Alta California, and then moved south to blockade the Pacific coast of Baja California. The Mexican government refused to be pressured into signing a peace treaty at this point, so the U.S. invaded the Mexican heartland and captured the capital, Mexico City, to force peace negotiations. 

The Treaty of Guadalupe Hidalgo, ending the Mexican-American War, was signed on February 2, 1848. The treaty called for the U.S. to pay $15 million to Mexico and pay off $3.25 million of claims of American citizens against Mexico. The treaty acknowledged that Mexico gave up its claims to Texas and gave the United States the Rio Grande as a boundary for Texas. 

The Mexican Cession gave the U.S. ownership of all of today’s California, Nevada, and Utah; most of Arizona, down to the Gila River; roughly half of New Mexico; and parts of Colorado and Wyoming. 

The entire Mexican Cession totaled 529,189 square miles (18%) at approximately five cents an acre.

The Mexican Cession of 1848 added vast new territories to the United States.

1853 - Gadsden Purchase 

As the railroad age evolved, business-oriented Americans realized that a non-mountainous, all-season southern transcontinental railroad route was desired. 

The draft of the Treaty of Mesilla, between Mexico and the United States, was signed on December 30, 1853, whereby the U.S. paid Mexico $10 million for the Gadsden Purchase, consisting of 29,670 square miles (1%) of today’s Arizona lands south of the Gila River and New Mexico lands west of the Rio Grande. The U.S. Congress and Mexican government approved the purchase in the first half of 1854. 

The 1853 Gadsden Purchase provided new lands for a southern transcontinental railroad.

The purchase was the last substantial territorial acquisition in the contiguous United States and defined the current U.S.-Mexican border. 

Delayed by the Civil War, the Southern Pacific Railroad completed the southern transcontinental railroad route in 1881-1883. 

1867 - Alaska Purchase 

Russian explorers first reached Alaska in 1733, and began establishing seal and sea otter hunting centers and fur trading-posts in the Aleutian Islands and along the Alaskan mainland coast. By the late 1790s, some of these had become permanent settlements. However, the Russians never fully colonized Alaska. For the most part, they clung to the coast and shunned the interior. 

Russian coastal settlements reached as far south as California, operating Fort Ross, just north of today’s San Francisco, from 1812-1841. 

The Russo-American Treaty of 1824 recognized exclusive Russian rights to the fur trade above parallel 50 degrees, 40 minutes north. Russia made a similar treaty with the British in 1825 that not only recognized the Russian fishing rights, but set the boundaries of Russian and British territorial possessions of the Pacific Coast, including the current eastern boundary of Alaska, along with the so-called Alaskan panhandle. 

But the Russian outposts were dependent upon British and American merchants for sorely-need food and supplies. 

By the 1860s, the Russian government was ready to abandon its Russian America colony. Zealous over-hunting had severely reduced the fur-bearing animal population, and competition from the British and Americans exacerbated the situation. This, combined with the difficulties of supplying and protecting such a distant colony, reduced their interest in the territory. Also, given America’s recent manifest destiny record, Russian was concerned that the U.S. might just take Alaska militarily. 

America was interested in Alaska because it believed Asia would become an important market for the country’s products, and expected that Alaska would serve as a base for American trade with Asia and globally, establishing America as a power in the Pacific. Also, occupying Alaska would prevent Russia and Britain from expanding into North America. 

Following the end of the American Civil War (1861-1865), the United States and Russia began negotiations that resulted in a treaty on March 30, 1867 that specified that the U.S. would buy Alaska from Russia for the price of $7.2 million, or two cents an acre. The purchase added 586,400 square miles (20% of the size of the continuous U.S.) to United States territory. 

The acquisition of Alaska added huge non-contiguous territory to the United States.

1898 - Hawaii Annexation 

British explorer Captain James Cook was the first European to visit the Hawaiian Islands, landing on a Kuai beach in 1778. By 1791, the native Kingdom of Hawaii had been established, and by 1810, extended to the seven major Hawaiian Islands. 

The sugar industry was introduced in Hawaii in the 1830s. Foreign business people were attracted to sugar investments and to exploit Hawaii’s sandal wood and whales. In the 1890s, pineapples and sugarcane became huge crops. Plantation workers were brought to Hawaii from Japan, China, and the Philippines. Great Britain, France, and the United States all had their eyes on the islands. In 1897, to enhance trade with the U.S., Hawaii signed a treaty giving the U.S. exclusive use of Pearl Harbor on the island of Oahu as a naval base.

Threatened by European nations wanting to add Hawaii to their empire, American businessmen in Hawaii began to seek annexation by the United States. Pro-American elements in Hawaii overthrew the monarchy on January 17, 1893, beginning a transition to U.S. control. The Republic of Hawaii was established in 1894. Hawaii was annexed by the U.S. in 1898, and became an official territory of the U.S. in 1900. 

The Hawaiian Islands, 2,400 miles off the West Coast of continguous America, added a total land are of about 6,400 square miles to U.S. territory. 

The Hawaiian Islands, 2,400 miles off  the West Coast, were annexed by the United States in 1898.

The United States Today 

The map below shows all 50 U.S. states along with the year each one became a state. 

Note that the statehood year for the original 13 colonies is not 1783, at the end of the Revolutionary War, but up to seven years later, depending on the time it took each state to ratify the United States Constitution, written in 1787. The last two states to attain statehood in the contiguous U.S. were New Mexico and Arizona in 1912. The two non-contiguous states, Alaska and Hawaii, didn’t attain statehood until 1959. 

The 50 states of the United States of America, along with their statehood dates.

The total area of the United States is 2,959,064 square miles with a 2020 population of about 330 million people.   

Territories of the U.S. 

Historically, U.S. territories were created to administer newly acquire land, and most eventually attained statehood. Others, such as the Philippines, Micronesia, the Marshall Islands, and Palau, later became independent.

The U.S. currently has 14 territories in the Caribbean Sea and the Pacific Ocean. Five of these territories are permanently inhabited: Puerto Rico, Guam, American Samoa, the U.S. Virgin Islands, and the Northern Mariana Islands. Each territory is self-governing. People in U.S. territories cannot vote for President of the United States, and they do not have full representation in the U.S. Congress. 

An overview of the five populated American territories is shown in the table below in the order each was acquired: 

Name	Acquired	How Acquired	Location	Area (square miles)	Population (2020)
Puerto Rico	1899	Ceded by Spain after Spanish-American War	Caribbean (North Atlantic)	3,515	3,193,694
Guam	1899	Ceded by Spain after Spanish-American War	Micronesia    (North Pacific)	210	168,485
American Samoa	1900	U.S. took control of eastern half of Samoan Islands after Second Samoan Civil War	Polynesia (South Pacific)	76	49,437
U.S. Virgin Islands	1917	Purchased from Denmark  for $25 million    (Main islands are Saint Thomas, Saint John, Saint Croix)	Caribbean (North Atlantic)	134	106,235
Northern Mariana Islands	1986	Conquered by U.S. during WWII.  In UN trusteeship until 1986, becoming U.S. commonwealth. (Main island is Saipan)	Micronesia (North Pacific)	179	51,433