1. Westward Expansion The tensions over slavery factored into other aspects of American politics and society, including westward expansion. Slavery was not the sole reason for American expansion. A common thread running through the country’s history has been its expansion westward. The War of 1812 resulted in Britain discontinuing its attempts to subsidize or support Native American tribes in the Ohio Valley or the Mississippi River Valley. This action helped secure the US’s ability to move westward, buying out or otherwise removing Native American tribes who inhabited the area. The removal did not go without controversy, as the several US wars with Native American tribes attest. The United States’ geographic location was an immense help in its movement westwards. Flanked by oceans, the United States had little fear of external invasion (with the exception of Great Britain in the War of 1812). Nor did the early presidents favor intervention in foreign politics. The Monroe Doctrine (Links to an external site.) of 1823 established that the US would not interfere in European colonies currently in existence in the Americas, but would not tolerate further European intervention or interference in the western hemisphere. The Monroe Doctrine had little practical effect in deterring European behavior, but neither did foreign countries press the matter. Peace with Britain was another advantage for the United States. The Treaty of Ghent opened the door for a US-British reconciliation of sorts: the US would no longer make moves to acquire British Canada, and Britain would not challenge US westward expansion in its commonly recognized borders. US-British relations were not perfect (particularly in the suppression of the international slave trade), but a series of treaties demonstrated US-British cooperation. The Rush-Bagot Treaty (Links to an external site.) of 1818 demilitarized the Great Lakes, established the current US-Canadian border west of the Great Lakes, and provided for joint occupation and government of disputed areas in the Oregon Territory. The Webster-Ashburton Treaty (Links to an external site.) of 1842 settled the Maine-New Brunswick boundary. 2. American Migration to Mexico and the Texas Revolution To the south, the Transcontinental Treaty (Links to an external site.) of 1819 (also known as the Adams-Onis Treaty) established a firm US-Mexican boundary—first with Spain, then with the independent Mexico.  Ironically, it was the migration of American citizens out of the United States that set the stage for the most contentious stage of American expansion. Following Mexico’s independence, Texas became part of the Mexican state of Coahuila y Tejas (the local name for the region). This area was in the far north of Mexico, and was sparsely inhabited. As part of a program to colonize the area, in the 1820s Mexico encouraged Americans settlers to migrate. Influential Americans like Stephen Austin (Links to an external site.) received large land.

1. 1. Westward Expansion
The tensions over slavery factored into other aspects of
American politics and society, including westward expansion.
Slavery was not the sole reason for American expansion. A
common thread running through the country’s history has been
its expansion westward. The War of 1812 resulted in Britain
discontinuing its attempts to subsidize or support Native
American tribes in the Ohio Valley or the Mississippi River
Valley. This action helped secure the US’s ability to move
westward, buying out or otherwise removing Native American
tribes who inhabited the area. The removal did not go without
controversy, as the several US wars with Native American tribes
attest.
The United States’ geographic location was an immense help in
its movement westwards. Flanked by oceans, the United States
had little fear of external invasion (with the exception of Great
Britain in the War of 1812). Nor did the early presidents favor
intervention in foreign politics. The Monroe Doctrine (Links to
an external site.) of 1823 established that the US would not
interfere in European colonies currently in existence in the
Americas, but would not tolerate further European intervention
or interference in the western hemisphere. The Monroe Doctrine
had little practical effect in deterring European behavior, but
neither did foreign countries press the matter.
Peace with Britain was another advantage for the United States.
The Treaty of Ghent opened the door for a US-British
reconciliation of sorts: the US would no longer make moves to
acquire British Canada, and Britain would not challenge US
westward expansion in its commonly recognized borders. US-
British relations were not perfect (particularly in the
suppression of the international slave trade), but a series of
treaties demonstrated US-British cooperation. The Rush-Bagot
Treaty (Links to an external site.) of 1818 demilitarized the
Great Lakes, established the current US-Canadian border west

2. of the Great Lakes, and provided for joint occupation and
government of disputed areas in the Oregon Territory. The
Webster-Ashburton Treaty (Links to an external site.) of 1842
settled the Maine-New Brunswick boundary.
2. American Migration to Mexico and the Texas Revolution
To the south, the Transcontinental Treaty (Links to an external
site.) of 1819 (also known as the Adams-Onis Treaty)
established a firm US-Mexican boundary—first with Spain, then
with the independent Mexico. Ironically, it was the migration
of American citizens out of the United States that set the stage
for the most contentious stage of American expansion.
Following Mexico’s independence, Texas became part of the
Mexican state of Coahuila y Tejas (the local name for the
region). This area was in the far north of Mexico, and was
sparsely inhabited. As part of a program to colonize the area, in
the 1820s Mexico encouraged Americans settlers to migrate.
Influential Americans like Stephen Austin (Links to an external
site.) received large land grants to bring others to Texas and
turn them into Mexican citizens.
Cotton, slavery, and American political ideals also accompanied
the Texas settlers. Mexico’s abolition of slavery did little
good—enslaved blacks were forced to sign lifetime contracts
that undid the law’s intent. The tumultuous nature of Mexico’s
politics also frustrated the acculturation process—white
American settlers identified politically, religiously, and
economically with the United States rather than with their new
homeland. White Texans watched nervously as Mexico’s central
government devolved into dictatorship and Mexico’s leadership
threatened to bring Texas to heel. Mexico’s attacks on the
Alamo (Links to an external site.) and Goliad (Links to an
external site.) in 1836 backfired when Texas forces defeated
Mexican troops at the Battle of San Jacinto (Links to an
external site.), and secured their independence. Texas declared

3. its independence from Mexico and Texans defended it while
seeking annexation to the United States.
3. Manifest Destiny
Americans observed Texas’s fight with Mexico with interest.
The Jackson and Van Buren administrations considered but then
rejected annexation of Texas because of Mexico’s opposition as
well as possible domestic controversy. Southern political
interests hoped for annexation since Texas represented a vast
slaveholding territory. Many Northern interests opposed
annexation for exactly the same reason.
Americans both North and South considered not just Texas, but
much of Mexico’s northern territories, as ripe for the taking. To
them, the slave/free controversy was secondary to the intent of
Providence, or “manifest destiny.” The concept of Manifest
Destiny (Links to an external site.) was that the US “overspread
the continent allotted by Providence for the free development of
our yearly multiplying millions,” in the words of journalist John
Louis O’Sullivan, who coined the term.
O’Sullivan’s exhortation included not just Texas, but Mexican
California and the Oregon Country (then jointly occupied with
Britain, a final disposition not yet resolved). It tied in with an
American sense of purpose and exceptionalism, and of
America’s commitment to progress and liberty. Mexico’s
political turmoil and the battle it had lost against Texans
seemed to confirm American exceptionalism. The presence of
Native American tribes and their claims on the land did not
inhibit the sense that expansion was inevitable and desirable.
4. Tension with Mexico, Compromise with Britain
Mexico’ government did not give up on recovering Texas after
its declaration of independence. Not only did national pride
play a role, but so did Texas’s expansive claims for its new

4. boundaries, south to the Rio Grande and west into New Mexico.
At the very least, Mexico expected the US to negotiate a final
resolution. But the Texas issue was too hot for the Van Buren or
Harrison/Tyler administrations to touch, so in the meantime
Texas remained the Lone Star Republic.
The presidential election of 1844 (Links to an external site.)
involved both the future of the Oregon territory and Texas. The
Whigs nominated Henry Clay, who opposed Texas annexation in
hopes of garnering Northern Whig votes. The Democrats
nominated James K. Polk of Tennessee. Polk’s campaign was
avowedly expansionist, and once Polk became president, he
acted upon that impulse.
The decisive step toward the annexation of Texas preceded
Polk’s inauguration. Outgoing President John Tyler requested
that Congress pass a resolution of annexation, which required a
simple majority, rather than a treaty which required the Senate’s
consent and would fail due to Northern opposition. Annexation
passed Congress by a close vote, and Texas became the twenty-
eighth state. Abolitionists and other Northern politicians feared
this represented the expansion of the “slave power” in national
politics. By the terms of annexation, Texas would be included
in the Missouri Compromise and any new states created from it
(a significant possibility given its size) would be slaveholding
states.
Mexico considered US annexation a breach of international law,
a sentiment shared by many Northern Whigs already opposed to
Texas’s admission as a slave state. Polk dispatched US military
forces into Texas to defend the state’s expansive territorial
claims. Such a move invited the inevitable response from
Mexico.
Meanwhile, controversy over the Oregon territory also came to
a head. Polk informed Britain that the US would end its joint
occupation and would organize Oregon according to US claims,
well above the Forty-Ninth Parallel (or as the slogan of the time
went, “54’40 or Fight!”). This tactic was partially a bluff,

5. designed to get Britain to compromise as the US was heading
into conflict with Mexico. In fact, that’s exactly what Britain
did in 1846.
Polk had secretly made offers to Mexico to resolve the Texas
dispute, but such offers came too late and were likely to be
rejected anyway. Fighting began in April 1846 when Mexican
forces attacked US troops in the contested area. This attack
gave Polk the justification to request a declaration of war,
stating, “Mexico has passed the boundary of the United States,
has invaded our territory and shed American blood upon the
American soil.” Congress did declare war, but that did not mean
the end of the debate.
“War fever” and patriotism sustained the war effort, but
opposition was not insignificant. Northern Whigs were
particularly opposed to the war. The Massachusetts legislature
voted a resolution against it, declaring:
Resolved, That such a war of conquest, so hateful in its objects,
so wanton, unjust, and unconstitutional in its origin an
character, must be regarded as a war against freedom, against
humanity, against injustice, against the Union, against the
Constitution, and against the Free States; and that a regard for
the true interests and the highest honor of the country, not less
than the impulses of Christian duty, should arouse all good
citizens to join in efforts to arrest this gigantic crime, by
withholding supplies, or other voluntary contributions, for its
further prosecution; by calling for the withdrawal of our army
within the established limits of the United States; and in every
just way aiding the country to retreat from the disgraceful
position of aggression which it now occupies toward a weak,
distracted neighbor and sister republic.
US forces—naval, the regular army, state militias, and
volunteers—outperformed expectations. Northern Mexico was
cleared of enemy forces within months. In California, US
settlers overthrew Mexican authority and declared the Bear Flag
Republic (Links to an external site.) in preparation for US
annexation. US forces moved into New Mexico and soon

6. occupied that region. By September 1847 US forces occupied
Mexico City. But Mexico’s crippled government was so hostile
to a settlement that the war continued on if only in name. It
ended in early 1848 with the signing of the Treaty of
Guadeloupe Hidalgo. The end result was that Mexico lost her
northern territories (nearly half of her total land area) and the
US grew by one-third.
6. The Wilmot Proviso Expands the Sectional Controversy
Northern Whigs largely opposed the war with Mexico. They
were angry that Polk compromised on Oregon while fighting for
Texas. Looking ahead, Whigs were concerned that future
acquisitions like California might become slave states (since
they were below the Missouri Compromise line) even though
they had been free territory under Mexican law. The greater fear
for many Northern politicians was that “free labor” was under
attack.
Shortly after the Mexican-American War began, Representative
David Wilmot of Pennsylvania wrote legislation to be attached
to a war funding measure. The Wilmot Proviso (Links to an
external site.) stated:
Provided, That, as an express and fundamental condition to the
acquisition of any territory from the Republic of Mexico by the
United States, by virtue of any treaty which may be negotiated
between them, and to the use by the Executive of the moneys
herein appropriated, neither slavery nor involuntary servitude
shall ever exist in any part of said territory, except for crime,
whereof the party shall first be duly convicted.
Even though the Proviso failed to pass Congress, its
introduction infuriated Southern politicians who saw it as an
attack of slaveholding states and a violation of the Missouri
Compromise. It angered Southern states against Northern states,
and also made Southern Whigs and Democrats more suspicious

7. of their Northern party counterparts. The grounds for sectional
compromise were eroding, slowly but surely.
7. The Implications of Manifest Destiny
The principles of Manifest Destiny included not just a physical
expansion of the United States, but an expansion of American
ideals. In large measure, those ideals were based an American
racial precepts. The Treaty of Guadeloupe Hidalgo assured
Mexicans in now-US territory that they could remain and
become US citizens, but many Americans considered that to be
a right in name only. Mexicans in the Southwest found
themselves in an American system that placed whites on top and
denied others equal treatment. Similarly, Native American
tribes in the Southwest faced more direct contact with American
migrants who considered the land to be US-owned. The
discovery of gold in California in 1848 (Links to an external
site.) at Sutter’s Mill stimulated Chinese immigration to the
region, along with thousands of Americans. This added another
wrinkle to social relations and the issue of civil rights and
liberties and these nineteenth-century precedents continued on
well into the twentieth century.
The US victory in the Mexican-American War also stoked
interest in further expansion. Southerners especially coveted
Cuba, then a Spanish colony with a long history of tropical
products and slavery. More ambitious Southerners engaged in
efforts to establish an American presence in Central and South
America. These largely failed, but demonstrates the durability
of slavery and the ability of Southerners to plan for its
expansion. These added to the sectional debate into the 1850s.